Patent Publication Number: US-11396670-B2

Title: Protein expression strains

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 16/624,616, filed on Dec. 19, 2019, which is a U.S. national stage application filed under U.S.C. § 371, based on International Patent Application No. PCT/EP2018/066344, filed on Jun. 20, 2018, which claims priority to EP Application No. 17176932.6, filed on Jun. 20, 2017. The entire contents of each of the foregoing applications, including all drawings and sequence listings, are hereby incorporated herein by reference. 
    
    
     REFERENCE TO SEQUENCE LISTING 
     The instant application contains a Sequence Listing which has been submitted electronically in ASCII format and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Sep. 1, 2021, is named 127042-11502_SeqListing.TXT and is 129,239 bytes in size. 
     FIELD OF THE INVENTION 
     This invention relates primarily to the development of fungal strains which express proteins at levels substantially higher than the parental strains. 
     BACKGROUND OF THE INVENTION 
     For some 30 years, desired heterologous proteins have been produced in microorganisms. However, having introduced the necessary coding sequence and obtained expression, much still remains to be done in order to optimise the process for commercial production. One area of interest concerns strain improvement, that is to say finding or making strains of the host microorganism which enable the protein to be made in higher yields or better purity, for example. 
     To increase the yield, once a good expression system has been devised, one might envisage trying to increase the copy number of the coding sequence, or to increase the quantity or stability of the mRNA, or to improve folding and/or secretion of the protein or to decrease the degradation of the protein. However, the desired effect of increased expression will only be seen if the limiting factor(s) is targeted. 
     Therefore, what is required is a host strain which allows the yield of a desired protein, such as a heterologous protein, to be increased. 
     The inventors have surprisingly identified that mutation of GSH1 in a fungal cell results in such an increased yield of heterologous protein. 
     The product of the GSH1 gene in  Saccharomyces cerevisiae  is γ-glutamylcysteine synthetase (Gsh1p). This enzyme catalyses the first, and rate-limiting, step in the synthesis of glutathione (L-γ-glutamylcysteinylglycine; GSH). The second step is catalysed by glutathione synthetase (Gsh2p). Glutathione is an essential molecule which has many important roles including protecting cells against oxidative stress, as a cofactor in several biosynthesis pathways and detoxification reactions, and maintenance of the yeast mitochondrial genome (Ayer et al (2010) Free Radical Biology &amp; Medicine 49 1956-1968)). Yeast cells deleted for the GSH1 gene, unless grown in media containing glutathione, are hypersensitive to a range of stress conditions, such as oxidative conditions and exposure to heavy metals and they eventually undergo growth arrest (Spector et al (2001) The Journal of Biological Chemistry 276 (10) 7011-7016). Glutathione is also known to protect the nucleus at times of oxidative stress (Hatem et al (2014) Free Radical Biology &amp; Medicine 67 103-114). Biterova and Barycki (2009) (The Journal of Biological Chemistry 284, 32700-32708) analyzed crystal structures of Ghs1 (also known as glutamate cysteine ligase) to investigate the mechanism of glutathione biosynthesis, and state that variants of human glutamate cysteine ligase have been observed (e. g. R127C, P158L, H370L and P414L). 
     Previously (PCT/US2016/068239), it was identified that mutation of NOT4 (also known as MOT2) results in an increased yield of heterologous protein produced in a host strain. The inventors have now identified that combining the NOT4 and GSH1 mutations surprisingly results in a further increase in yield. 
     Not4 is a ubiquitin-ligating enzyme and is part of the Ccr4-Not complex. The Ccr4-Not complex is conserved in eukaryotic cells, and in yeast the complex consists of 9 core subunits: Ccr4, Caf1, Caf40, Caf130, Not1, Not2, Not3, Not4 and Not5 (Collart, 2003, Global control of gene expression in yeast by the Ccr4-Not complex.  Gene  313: 1-16; Bai et al, 1999, The CCR4 and Caf1 proteins of the Ccr4-Not complex are physically and functionally separated from Not2, Not4, and Not5.  Mol. Cell. Biol.  19: 6642-6651). The complex has been proposed to function as a central switchboard that can interpret signals from the environment and coordinate all levels of gene expression to economically respond to the signal (Collart, 2012, The Ccr4-Not complex.  Gene  492(1): 42-53). It is thought that Not proteins (Not1, Not2, Not3, Not4) are necessary for assembly of the RNA polymerase II complex, which suggests a global role in transcription regulation (Collart, 1994, Not1 (cdc39), Not2(cdc36), Not3, and Not4 encode a global-negative regulator of transcription that differentially affects tata-element utilization.  Genes  &amp;  Development  8(5): 525-537; Collart, 2012, as cited above). A co-crystal structure suggested how the C-terminal region of Not4 wraps around a HEAT-repeat region of Not1, the scaffold protein in the Ccr4-Not complex (Bhaskar, 2015, Architecture of the ubiquitylation module of the yeast Ccr4-Not complex.  Structure  23(5): 921-8). 
     SUMMARY OF THE INVENTION 
     The invention provides a fungal host cell having: 
     a. a modified Gsh1 protein or homolog thereof, and/or 
     b. a modified activity level of Gsh1 protein or homolog thereof, and/or 
     c. a modified GSH1 gene or homolog thereof, and/or 
     d. a modified level of expression of GSH1 gene or homolog thereof. 
     The invention also provides a fungal host cell further having: 
     e. a modified Not4 protein or homolog thereof, and/or 
     f. a modified activity level of Not4 protein or homolog thereof, and/or 
     g. a modified NOT4 gene or homolog thereof, and/or 
     h. a modified level of expression of NOT4 gene or homolog thereof. 
     The invention also provides a culture of fungal host cells containing a polynucleotide sequence encoding a desired protein, such as a heterologous protein, characterised in that the fungal host cells have a reduced activity level and/or expression level of Gsh1 protein of homolog thereof, and optionally further having a reduced activity level and/or expression level of Not4 protein or homolog thereof. 
     The invention further provides a method for producing a desired protein, such as a heterologous protein, from a fungal host cell. 
     The invention provides a method for modifying the production yield of a desired polypeptide from a fungal host cell. 
     The invention also provides a desired protein, such as a heterologous protein. Albumin or variant, fragment, and/or fusion thereof is a preferred desired protein. 
     The invention further provides a composition, such as a pharmaceutical composition, comprising the desired protein. 
     The invention also provides a method of treating a patient comprising administering an effective amount of the composition to the patient. 
     The invention further provides a method of preparing a fungal host cell having the above mentioned property or properties. 
     The invention also provides a Gsh1 protein or homolog thereof comprising at least 50% identity to SEQ ID NO: 2 and a mutation at a position corresponding to one or more positions selected from 47, 48, 49, 50, 51, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 409, 451, 452, 453, 454 and 455 of SEQ ID NO: 2. 
     The invention further provides a polynucleotide encoding a Gsh1 variant of the present invention. 
     Any embodiments described herein, including those described only in the examples and/or the Preferred Embodiments section, are intended to be able to combine with any other embodiments, unless explicitly disclaimed or the combination is improper. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a Venn diagram showing the classes of and relationship between twenty amino acids. 
         FIG. 2  shows the construction of plasmid pDB5438. 
         FIG. 3  shows the construction of plasmid pDB2305, “HSA” means recombinant human albumin, “mFL” is a leader sequence. 
         FIG. 4  shows the construction of plasmid pDB2244, “rHA” means recombinant human albumin, “FL” is a leader sequence. 
         FIG. 5  shows the construction of plasmid YCp50. 
         FIG. 6  shows the construction of plasmid pDB5862. “Albumin variant” is nucleic acid encoding SEQ ID NO: 45. “mFL” is a leader sequence. 
         FIG. 7  shows the construction of plasmid pDB3936. 
         FIG. 8  shows the construction of plasmid pDB5912. “mFL” is a leader sequence. 
         FIG. 9  shows the construction of plasmid pDB3029. “Inv” is a leader sequence. 
     
    
    
     DEFINITIONS 
     Albumin: The term “albumin” means a protein having the same and/or very similar tertiary structure as human serum albumin (HSA) or HSA domains and has similar properties to HSA or the relevant domains. Similar tertiary structures are, for example, the structures of the albumins from the species mentioned under “parent albumin”. Some of the major properties of albumin are i) its ability to regulate plasma volume (oncotic activity), ii) a long plasma half-life of around 19 days±5 days, iii) binding to gp60, also known as albondin iv) binding to FcRn, v) ligand-binding, e.g. binding of endogenous molecules such as acidic, lipophilic compounds including bilirubin, fatty acids, hemin and thyroxine (see also Table 1 of Kragh-Hansen et al, 2002, Biol. Pharm. Bull. 25, 695, hereby incorporated herein by reference), vi) binding of small organic compounds with acidic or electronegative features e.g. drugs such as warfarin, diazepam, ibuprofen and paclitaxel (see also Table 1 of Kragh-Hansen et al, 2002, Biol. Pharm. Bull. 25, 695, hereby incorporated herein by reference). Not all of these properties need to be fulfilled to characterize a protein or fragment as an albumin. If a fragment, for example, does not comprise a domain responsible for binding of certain ligands or organic compounds the variant of such a fragment will not be expected to have these properties either. 
     Allelic variant: The term “allelic variant” means any of two or more alternative forms of a gene occupying the same chromosomal locus. Allelic variation arises naturally through mutation, and may result in polymorphism within populations. Gene mutations can be silent (no change in the encoded polypeptide) or may encode polypeptides having altered amino acid sequences. An allelic variant of a polypeptide is a polypeptide encoded by an allelic variant of a gene. 
     cDNA: The term “cDNA” means a DNA molecule that can be prepared by reverse transcription from a mature, spliced, mRNA molecule obtained from a eukaryotic or prokaryotic cell. cDNA lacks intron sequences that may be present in the corresponding genomic DNA. The initial, primary RNA transcript is a precursor to mRNA that is processed through a series of steps, including splicing, before appearing as mature spliced mRNA. 
     Coding sequence: The term “coding sequence” means a polynucleotide, which directly specifies the amino acid sequence of a polypeptide. The boundaries of the coding sequence are generally determined by an open reading frame, which begins with a start codon such as ATG, GTG or TTG and ends with a stop codon such as TAA, TAG, or TGA. The coding sequence may be a genomic DNA, cDNA, synthetic DNA, or a combination thereof. 
     Control sequences: The term “control sequences” means nucleic acid sequences necessary for expression of a polynucleotide encoding a polypeptide of the present invention. Each control sequence may be native (i.e., from the same gene) or foreign (i.e., from a different gene) to the polynucleotide encoding the polypeptide or native or foreign to each other. Such control sequences include, but are not limited to, a leader, polyadenylation sequence, pro-peptide sequence, promoter, signal peptide sequence, and transcription terminator. At a minimum, the control sequences include a promoter, and transcriptional and translational stop signals. The control sequences may be provided with linkers for the purpose of introducing specific restriction sites facilitating ligation of the control sequences with the coding region of the polynucleotide encoding a polypeptide. 
     Expression: The term “expression” includes any step involved in the production of a polypeptide including, but not limited to, transcription, post-transcriptional modification, translation, post-translational modification, and secretion. 
     Expression cassette: The term “expression cassette” means the polynucleotide encoding a polypeptide and the upstream and downstream control sequences that provide for its expression. 
     Expression host: The term “expression host” means any host cell that expresses a desired protein, particularly a heterologous protein. 
     Expression vector: The term “expression vector” means a linear or circular DNA molecule that comprises a polynucleotide encoding a polypeptide and is operably linked to control sequences that provide for its expression. 
     Fragment: The term “fragment” means a polypeptide having one or more (several) amino acids deleted from the amino and/or carboxyl terminus of a mature polypeptide and/or from an internal region of a mature polypeptide. Fragments may consist of one uninterrupted sequence derived from a polypeptide or may comprise two or more sequences derived from different parts of the polypeptide. With respect to albumin, a fragment may have a size of more than approximately 20 amino acid residues, preferably more than 30 amino acid residues, more preferred more than 40 amino acid residues, more preferred more than 50 amino acid residues, more preferred more than 75 amino acid residues, more preferred more than 100 amino acid residues, more preferred more than 200 amino acid residues, more preferred more than 300 amino acid residues, even more preferred more than 400 amino acid residues and most preferred more than 500 amino acid residues. In a preferred embodiment, a fragment corresponds to one or more of the albumin domains. Preferred albumin domains of the invention are domains having at least 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, 99.5% or 100% identity to a HSA domain I consisting of amino acid residues 1 to 194±1 to 15 amino acids of SEQ ID NO: 10; at least 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, 99.5% or 100% identity to HSA domain II consisting of amino acid residues 192 to 387±1 to 15 amino acids of SEQ ID NO: 10 and at least 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, 99.5% or 100% identity to HSA domain III consisting of amino acid residues 381 to 585±1 to 15 amino acids of SEQ ID NO: 10 or a combination of one or more (several) of these domains, e.g. domain I and II, domain II and III or domain I and III fused together. No generally accepted convention for the exact borders of the albumin domains exists and the overlap in the above mentioned ranges and the allowance of a varying length of plus or minus 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15 from amino acids, preferably from 1 to 15 amino acids, more preferably from 1 to 10 amino acids, most preferably from 1 to 5 amino acids, at the N-terminal and/or C-terminal of the domains, allowing for a total variance in length of up to 30 amino acids, preferably up to 20 amino acids, more preferably up to 10 amino acids for each domain reflects this fact and that there may be some diverging opinions on the amino acid residues in the border between the domains belonging to one or the other domain. For the same reason, it may be possible to find references to the amino acid residues of albumin domains that diverge from the numbers above, however, the skilled person will appreciate how to identify the albumin domains based on the teaching in the literature and the teaching above. Corresponding domains of non-human albumins can be identified by alignment with HSA using the Needleman-Wunsch algorithm (Needleman and Wunsch, 1970, J. Mol. Biol. 48: 443-453) as implemented in the Needle program of the EMBOSS package (EMBOSS: The European Molecular Biology Open Software Suite, Rice et al., 2000, Trends Genet. 16: 276-277), preferably version 3.0.0 or later, more preferably version 5.0.0 or later. The optional parameters used are gap open penalty of 10, gap extension penalty of 0.5, and the EBLOSUM62 (EMBOSS version of BLOSUM62) substitution matrix. Alternative alignment tools can also be used, for example MUSCLE as described herein. The domains may also be defined according to Dockal or Kjeldsen: Dockal et al (The Journal of Biological Chemistry, 1999, Vol. 274(41): 29303-29310) defines the domains of HSA as: Domain I: amino acids 1 to 197, Domain II: amino acids 189 to 385 of SEQ ID NO: 10, Domain III: amino acids 381 to 585 of SEQ ID NO: 10 Kjeldsen et al (Protein Expression and Purification, 1998, Vol 13: 163-169) defines the domains as: Domain I: amino acids 1 to 192, Domain II: amino acids 193 to 382, Domain III: amino acids 383 to 585. Each domain is itself made up of two homologous subdomains namely 1-105, 120-194, 195-291, 316-387, 388-491 and 512-585, with flexible inter-subdomain linker regions comprising residues Lys106 to Glu119, Glu292 to Va1315 and Glu492 to Ala511. 
     Therefore, in this invention, the following domain definitions are preferred. The amino acid numbers correspond to those of SEQ ID NO: 10 (HSA). However, using these numbers, the skilled person can identify corresponding domains in other albumin sequences. Domain I may or may not start at amino acid 1 and may or may not end at any of amino acids 192, 193, 194, 195, 196 or 197, preferably any of amino acids 192, 194 or 197. Domain II may or may not start at amino acid 189, 190, 191, 192 or 193, preferably any of amino acids 189, 192 or 193, and may or may not end at amino acid 382, 383, 384, 385, 386 or 387, preferably any of amino acids 382, 285 or 387. Domain III may or may not start at amino acid 381, 382 or 383, preferably amino acid 381 or 383, and may or may not end at amino acid 585. Domains in non-human albumins may have the same or different amino acid lengths and/or residue numbers as HSA. For example, a multiple alignment or pair-wise alignment may be prepared using HSA and one or more (several) other albumins, fragments, derivatives, variants and/or fusions in order to identify domains corresponding to domains I, II and/or III of HSA. 
     Fusion partner: Throughout this specification, a fusion partner is a non-albumin moiety which may be genetically fused to an albumin or variant and/or fragment thereof. 
     Heterologous protein: a heterologous protein is one not naturally produced by the host cell and, preferably, does not include proteins such as selection markers (e.g. antibiotic resistance markers, auxotrophic selectable markers), chaperones, FLP, REP1, or REP2. 
     Host cell: The term “host cell” means any cell type that is susceptible to transformation, transfection, transduction, or the like with a nucleic acid construct or expression vector comprising a polynucleotide of the present invention. The term “host cell” encompasses any progeny of a parent cell that is not identical to the parent cell due to mutations that occur during replication. 
     Mature polypeptide: The term “mature polypeptide” means a polypeptide in its final form following translation and any post-translational modifications, such as N-terminal processing, C-terminal truncation, glycosylation, phosphorylation, etc. The mature sequence of human albumin is provided in SEQ ID NO: 10, while an example of an immature form is provided in SEQ ID NO: 12. 
     Mature polypeptide coding sequence: The term “mature polypeptide coding sequence” means a polynucleotide that encodes a mature polypeptide. An example of a mature polypeptide coding sequence of human albumin is provided in SEQ ID NO: 9, while an example of a coding sequence for an immature form of human albumin is provided in SEQ ID NO: 11. 
     Mutant: The term “mutant” means a polynucleotide encoding a variant. 
     Nucleic acid construct: The term “nucleic acid construct” means a nucleic acid molecule, either single- or double-stranded, which is isolated from a naturally occurring gene or is modified to contain segments of nucleic acids in a manner that would not otherwise exist in nature or which is synthetic, which comprises one or more control sequences. 
     Operably linked: The term “operably linked” means a configuration in which a control sequence is placed at an appropriate position relative to the coding sequence of a polynucleotide, such that the control sequence directs expression of the coding sequence. 
     Parent or Parent Albumin: The term “parent” or “parent albumin” means an albumin to which an alteration is made to produce the albumin variants of the present invention. The parent may be a naturally occurring (wild-type) polypeptide or an allele thereof or a variant thereof. In a preferred embodiment, the parent albumin is a wild-type albumin, more preferably a wild-type albumin from  Homo sapiens  as disclosed in SEQ ID NO: 12 (UNIPROT: P02768.2) or the mature sequence thereof (SEQ ID NO: 10). Alternative wild-type albumins can be selected from the non-exhaustive list shown in Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Wild-type albumins from various species. 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 SwissProt or 
                 % Identity 
                   
               
               
                 Common 
                   
                 GenBank 
                 to SEQ ID 
                 Length 
               
               
                 Name 
                 Species 
                 Accession No 
                 NO: 10* 
                 (aa) 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Human 
                 
                   Homo sapiens 
                 
                 P02768.2 
                 100.0 
                 609 
               
               
                 Chimpanzee 
                 
                   Pan troglodytes 
                 
                 XP_517233 
                 98.8 
                 609 
               
               
                   
                   
                 (predicted 
                   
                   
               
               
                   
                   
                 sequence) 
                   
                   
               
               
                 Sumatran 
                 
                   Pongo abelii 
                 
                 Q5NVH5.2 
                 98.5 
                 609 
               
               
                 Orangutan 
                   
                   
                   
                   
               
               
                 Macaque 
                 
                   Macaca mulatta 
                 
                 Q28522.1 
                 93.3 
                 600 
               
               
                 (Rhesus 
                   
                   
                   
                   
               
               
                 Monkey) 
                   
                   
                   
                   
               
               
                 Cat 
                 
                   Felis catus 
                 
                 P49064.1 
                 81.9 
                 608 
               
               
                 Dog 
                 
                   Canis lupus 
                 
                 P49822.3 
                 80.0 
                 608 
               
               
                   
                 
                   familiaris 
                 
                   
                   
                   
               
               
                 Donkey 
                 
                   Equus asinus 
                 
                 Q5XLE4.1 
                 76.7 
                 607 
               
               
                 Horse 
                 
                   Equus caballus 
                 
                 P35747.1 
                 76.3 
                 607 
               
               
                 Blood fluke 
                 
                   Schistosoma 
                 
                 Q95VB7 
                 76.2 
                 608 
               
               
                   
                 
                   mansoni 
                 
                   
                   
                   
               
               
                 Bovine 
                 
                   Bos taurus 
                 
                 P02769.4 
                 75.6 
                 607 
               
               
                   
                   
                 (NP_851335.1) 
                   
                   
               
               
                 Pig 
                 
                   Sus scrota 
                 
                 P08835.2 
                 75.1 
                 607 
               
               
                 Sheep 
                 
                   Ovis aries 
                 
                 P14639.1 
                 75.0 
                 607 
               
               
                 Goat 
                 
                   Capra hircus 
                 
                 ACF10391.1 
                 74.8 
                 607 
               
               
                 Rabbit 
                 
                   Oryctolagus 
                 
                 P49065.2 
                 74.3 
                 608 
               
               
                   
                 
                   cuniculus 
                 
                   
                   
                   
               
               
                 Mongolian 
                 
                   Meriones 
                 
                 O35090.1 
                 73.6 
                 609 
               
               
                 Gerbil 
                 
                   unguiculatus 
                 
                   
                   
                   
               
               
                 Rat 
                 
                   Rattus norvegicus 
                 
                 P02770. 2. 
                 73.3 
                 608 
               
               
                 Mouse 
                 
                   Mus musculus 
                 
                 P07724.3. 
                 72.3 
                 608 
               
               
                 Guinea Pig 
                 
                   Cavia porcellus 
                 
                 Q6WDN9 
                 72.1 
                 608 
               
               
                 Chicken 
                 
                   Gallus gallus 
                 
                 P19121.2 
                 47.0 
                 615 
               
               
                   
               
               
                 *Sequence identity was calculated using the Needleman-Wunsch algorithm as implemented in the Needle program of EBLOSUM62 (EMBOSS suite of programs, version 6.1.0) using gap open penalty of 10, gap extension penalty of 0.5 as described herein. 
               
            
           
         
       
     
     Preferably the parent albumin is a mature albumin. In another embodiment, the parent albumin is at least 70%, more preferably 75%, more preferably at least 80%, more preferably at least 85%, even more preferably at least 90%, most preferably at least 95%, at least 96%, at least 97%, at least 98%, at least 99% at least 99.5% or at least 99.8% identical to SEQ ID NO: 10, and maintains at least one of the major properties of albumin or a similar tertiary structure as albumin, such as HSA. Major properties of albumin are summarized in Sleep, 2015, “Albumin and its application in drug delivery”, Expert Opinion on Drug Delivery 12(5): 793-812 (incorporated herein by reference). 
     Sequence identity: The relatedness between two amino acid sequences or between two nucleotide sequences is described by the parameter “sequence identity”. 
     For purposes of the present invention, the sequence identity between two amino acid sequences is determined using the Needleman-Wunsch algorithm (Needleman and Wunsch, 1970 , J. Mol. Biol.  48: 443-453) as implemented in the Needle program of the EMBOSS package (EMBOSS: The European Molecular Biology Open Software Suite, Rice et al., 2000 , Trends Genet.  16: 276-277), preferably version 5.0.0 or later. The parameters used are gap open penalty of 10, gap extension penalty of 0.5, and the EBLOSUM62 (EMBOSS version of BLOSUM62) substitution matrix. The output of Needle labeled “longest identity” (obtained using the −nobrief option) is used as the percent identity and is calculated as follows:
 
(Identical Residues×100)/(Length of Alignment−Total Number of Gaps in Alignment)
 
     For purposes of the present invention, the sequence identity between two deoxyribonucleotide sequences is determined using the Needleman-Wunsch algorithm (Needleman and Wunsch, 1970, supra) as implemented in the Needle program of the EMBOSS package (EMBOSS: The European Molecular Biology Open Software Suite, Rice et al., 2000, supra), preferably version 5.0.0 or later. The parameters used are gap open penalty of 10, gap extension penalty of 0.5, and the EDNAFULL (EMBOSS version of NCBI NUC4.4) substitution matrix. The output of Needle labeled “longest identity” (obtained using the −nobrief option) is used as the percent identity and is calculated as follows:
 
(Identical Deoxyribonucleotides×100)/(Length of Alignment−Total Number of Gaps in Alignment)
 
     Variant: The term “variant” means a polypeptide derived from a parent polypeptide, e.g. albumin, comprising an alteration, i.e., a substitution, insertion, and/or deletion, at one or more (several) positions. A substitution means a replacement of an amino acid occupying a position with a different amino acid; a deletion means removal of an amino acid occupying a position; and an insertion means adding 1-3 amino acids adjacent to an amino acid occupying a position. The altered polypeptide (variant) can be obtained through human intervention by modification of the polynucleotide sequence encoding the parental polypeptide, e.g. albumin. The variant albumin is preferably at least 70%, preferably at least 75%, more preferably at least 80%, more preferably at least 85%, even more preferably at least 90%, most preferably at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, at least 99.5% or at least 99.8% identical to SEQ ID NO: 10 and may or may not maintain at least one of the major properties of the parent albumin or a similar tertiary structure such as HSA. Generally, variants or fragments of HSA will have at least 10% (preferably at least 50%, 60%, 70%, 80%, 90% or 95%) of HSA ligand binding activity (for example bilirubin-binding) and at least 50% (preferably at least 70%, 80%, 90% or 95%) of HSA&#39;s oncotic activity, weight for weight. Oncotic activity, also known as colloid osmotic pressure, of albumin, albumin variants or fragments of albumin may be determined by the method described by Hoefs, J. C. (1992)  Hepatology  16:396-403 (incorporated herein by reference). Bilirubin binding may be measured by fluorescence enhancement at 527 nm relative to HSA. Bilirubin (1.0 mg) is dissolved in 50 microL of 1M NaOH and diluted to 1.0 mL with demineralised water. The bilirubin stock is diluted in 100 mM Tris-HCl pH8.5, 1 mM EDTA to give 0.6 nmol of bilirubin/mL in a fluorometer cuvette. Fluorescence is measured by excitation at 448 nm and emission at 527 nm (10 nm slit widths) during titration with HSA over a range of HSA:bilirubin ratios from 0 to 5 mol:mol. The variant may have altered binding affinity to FcRn and/or an altered plasma half-life when compared to the parent albumin. 
     With respect to a variant Gsh1 protein, the same principles apply, with the exception that activity is Gsh1 activity rather than albumin activity. The parent Gsh1 protein may have at least 50, 60, 70, 80 or 90% identity to SEQ ID NO: 2, more preferably 100% identity to SEQ ID NO: 2. The variant Gsh1 protein may have at least 50, 60, 70, 80, 85, 90, 95, 96, 97, 98, or at least 99% identity to SEQ ID NO: 2. 
     With respect to a variant Not4 protein, the same principles apply, with the exception that activity is Not4 activity rather than albumin activity. The parent Not4 protein may have at least 50, 60, 70, 80 or 90% identity to SEQ ID NO: 6, more preferably 100% identity to SEQ ID NO: 6. The variant Not4 protein may have at least 50, 60, 70, 80, 85, 90, 95, 96, 97, 98, or at least 99% identity to SEQ ID NO: 6. 
     The variant polypeptide sequence is preferably one which is not found in nature. 
     Vector: The term “vector” means a linear or circular DNA molecule that comprises a polynucleotide encoding a polypeptide and is operably linked to control sequences that provide for its expression. Vectors include plasmids. Vectors include expression vectors. 
     Wild-type: The term “wild-type” (WT) albumin means an albumin having the same amino acid sequence as the albumins naturally found in an animal or in a human being. SEQ ID NO: 10 is an example of a wild-type albumin from  Homo sapiens . The “wild-type” human albumin (HSA) sequence is given by GenBank Accession number AAA98797.1 (Minghetti et al. “Molecular structure of the human albumin gene is revealed by nucleotide sequence within q11-22 of chromosome 4”, J. Biol. Chem. 261 (15), 6747-6757 (1986), incorporated herein by reference). Examples of wild-type albumins are provided in Table 1 (above). 
     Conventions for Designation of Amino Acid Positions 
     For purposes of the present invention, the polypeptide disclosed in SEQ ID NO: 2 is used to determine the corresponding amino acid residue in a homolog of Gsh1 protein. The amino acid sequence of a homolog of Gsh1 protein is aligned with the polypeptide disclosed in SEQ ID NO: 2, and based on the alignment, the amino acid position number corresponding to any amino acid residue in the polypeptide disclosed in SEQ ID NO: 2 is determined using the Needleman-Wunsch algorithm (Needleman and Wunsch, 1970 , J. Mol. Biol.  48: 443-453) as implemented in the Needle program of the EMBOSS package (EMBOSS: The European Molecular Biology Open Software Suite, Rice et al., 2000 , Trends Genet.  16: 276-277), preferably version 5.0.0 or later. The parameters used are gap open penalty of 10, gap extension penalty of 0.5, and the EBLOSUM62 (EMBOSS version of BLOSUM62) substitution matrix. The same principles can be used in relation to Not4, based on SEQ ID NO: 6. 
     Identification of the corresponding amino acid residue in a homolog of Gsh1 protein can be determined by an alignment of multiple polypeptide sequences using several computer programs including, but not limited to, MUSCLE (multiple sequence comparison by log-expectation; version 3.5 or later; Edgar, 2004 , Nucleic Acids Research  32: 1792-1797), MAFFT (version 6.857 or later; Katoh and Kuma, 2002 , Nucleic Acids Research  30: 3059-3066; Katoh et al., 2005 , Nucleic Acids Research  33: 511-518; Katoh and Toh, 2007 , Bioinformatics  23: 372-374; Katoh et al., 2009 , Methods in Molecular Biology  537: 39-64; Katoh and Toh, 2010 , Bioinformatics  26: 1899-1900), and EMBOSS EMMA employing ClustalW (1.83 or later; Thompson et al., 1994 , Nucleic Acids Research  22: 4673-4680), using their respective default parameters. The same principles can be used in relation to Not4, based on SEQ ID NO: 6. 
     In describing the polypeptides of the present invention, the nomenclature described below is adapted for ease of reference. The accepted IUPAC single letter or three letter amino acid abbreviation is employed. 
     Substitutions. For an amino acid substitution, the following nomenclature is used: Original amino acid, position, substituted amino acid. Accordingly, the substitution of threonine at position 226 with alanine is designated as “Thr226Ala” or “T226A”. Multiple mutations are separated by addition marks (“+”), e.g., “Gly205Arg+Ser411Phe” or “G205R+5411 F”, representing substitutions at positions 205 and 411 of glycine (G) with arginine (R) and serine (S) with phenylalanine (F), respectively. 
     Deletions. For an amino acid deletion, the following nomenclature is used: Original amino acid, position, *. Accordingly, the deletion of glycine at position 195 is designated as “Gly195*” or “G195*”. Multiple deletions are separated by addition marks (“+”), e.g., “Gly195*+Ser411*” or “G195*+S411*”. 
     Insertions. As disclosed above, an insertion may be to the N-side (‘upstream’, ‘X-1’) or C-side (‘downstream’, ‘X+1’) of the amino acid occupying a position (‘the named (or original) amino acid’, ‘X’). 
     For an amino acid insertion to the C-side (‘downstream’, ‘X+1’) of the original amino acid (‘X’), the following nomenclature is used: Original amino acid, position, original amino acid, inserted amino acid. Accordingly, the insertion of lysine after glycine at position 195 is designated “Gly195GlyLys” or “G195GK”. An insertion of multiple amino acids is designated [Original amino acid, position, original amino acid, inserted amino acid #1, inserted amino acid #2; etc.]. For example, the insertion of lysine and alanine after glycine at position 195 is indicated as “Gly195GlyLysAla” or “G195GKA”. 
     In such cases the inserted amino acid residue(s) are numbered by the addition of lower case letters to the position number of the amino acid residue preceding the inserted amino acid residue(s). In the above example, the sequence would thus be: 
     
       
         
           
               
               
               
             
               
                   
               
               
                   
                 Parent: 
                 Variant: 
               
               
                   
               
             
            
               
                   
                 195 
                 195 195a 195b 
               
               
                   
                 G 
                 G - K - A 
               
               
                   
               
            
           
         
       
     
     For an amino acid insertion to the N-side (‘upstream’, ‘X-1’) of the original amino acid (X), the following nomenclature is used: Original amino acid, position, inserted amino acid, original amino acid. Accordingly, the insertion of lysine (K) before glycine (G) at position 195 is designated “Gly195LysGly” or “G195KG”. An insertion of multiple amino acids is designated [Original amino acid, position, inserted amino acid #1, inserted amino acid #2; etc., original amino acid]. For example, the insertion of lysine (K) and alanine (A) before glycine at position 195 is indicated as “Gly195LysAlaGly” or “G195KAG”. In such cases the inserted amino acid residue(s) are numbered by the addition of lower case letters with prime to the position number of the amino acid residue following the inserted amino acid residue(s). In the above example, the sequence would thus be: 
     
       
         
           
               
               
               
             
               
                   
               
               
                   
                 Parent: 
                 Variant: 
               
               
                   
               
             
            
               
                   
                 195 
                 195a′ 195b′ 195 
               
               
                   
                 G 
                 K - A - G 
               
               
                   
               
            
           
         
       
     
     Multiple alterations. Polypeptides comprising multiple alterations are separated by addition marks (“+”), e.g., “Arg170Tyr+Gly195Glu” or “R170Y+G195E” representing a substitution of arginine and glycine at positions 170 and 195 with tyrosine and glutamic acid, respectively. 
     Different alterations. Where different alterations can be introduced at a position, the different alterations are separated by a comma, e.g., “Arg170Tyr,Glu” represents a substitution of arginine at position 170 with tyrosine or glutamic acid. Thus, “Tyr167Gly,Ala+Arg170Gly,Ala” designates the following variants: 
     “Tyr167Gly+Arg170Gly”, “Tyr167Gly+Arg170Ala”, “Tyr167Ala+Arg170Gly”, and “Tyr167Ala+Arg170Ala”. 
     DETAILED DESCRIPTION OF THE INVENTION 
     A first aspect of the invention provides a fungal host cell having: 
     a. a modified Gsh1 protein or homolog thereof, and/or 
     b. a modified level of activity of Gsh1 protein or homolog thereof, and/or 
     c. a modified GSH1 gene or homolog thereof, and/or 
     d. a modified level of expression of GSH1 gene or homolog thereof. 
     The modified Gsh1 protein may be modified relative to a reference Gsh1 protein such as a wild-type Gsh1 protein for example SEQ ID NO: 2. Preferably, the modified Gsh1 protein or homolog thereof has at least 50% identity to SEQ ID NO: 2, more preferably at least 55, 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, 99.1, 99.2, 99.3, 99.4, 99.5, 99.6, 99.7, 99.8 or at least 99.9% identity to SEQ ID NO: 2. The modified Gsh1 protein or homolog thereof may or may not have at most 99.9, 99.8, 99.7, 99.6, 99.5, 99.4, 99.3, 99.2, 99.1, 99, 98, 97, 96, 95, 90, 85, 80, 75, 70, 65, or at most 60% identity to SEQ ID NO: 2. More preferably, the modified Gsh1 protein comprises or consists of SEQ ID NO: 4. 
     It is preferred that the modified level of Gsh1 protein or homolog thereof is a reduced expression level of Gsh1 protein or homolog thereof and/or a reduced activity level of Gsh1 protein or homolog thereof. Preferably the modified, e.g. reduced, level is relative to the level in a reference fungal host cell, such as a fungal host cell in which the Gsh1 protein comprises or consists of SEQ ID NO: 2. The Gsh1 protein of the reference fungal host may be a wild-type Gsh1 sequence, such as SEQ ID NO: 2. A suitable reference fungal host cell is  S. cerevisiae  S288C or  S. cerevisiae  DXY1. S288C has the genotype MATα SUC2 gal2 mal2 mel flo1 flo8-1 hap1 ho bio1 bio6. DXY1 has the genotype leu2-3, leu2-122, can1, pra1, ubc4, ura3:yap3 (Kerry-Williams et al. (1998) Yeast 14:161-169, incorporated herein by reference). Other suitable reference fungal host cells include cells which are identical to the host cell with the exception of the GSH1 gene or Gsh1 protein or homolog thereof. For example, the GSH1 gene of the reference may be wild-type (e.g. SEQ ID NO: 1) or the GSH1 gene of the reference may encode wild-type Gsh1 protein (e.g. SEQ ID NO: 2) or the Gsh1 protein encoded by the reference may be wild-type (e.g. SEQ ID NO: 2). Preferably, the host cell of the invention is identical to a parent strain with the exception of the GSH1 gene or Gsh1 protein or homolog thereof. A reference fungal host may also be referred to as a “corresponding” fungal host. A reference fungal host may be a parent fungal host. 
     A reduced level of Gsh1 protein and/or activity level of Gsh1 protein may be achieved, for example, by mutating or deleting the GSH1 gene, thus resulting in a mutated Gsh1 protein or homolog thereof or complete absence of Gsh1 protein or homolog thereof; by removing or changing the open reading frame of the gene; by mutating or changing control sequences of the GSH1 gene such as a promoter sequence and/or a terminator sequence; by blocking or reducing transcription of the GSH1 gene for example by introducing suitable interfering RNA such as antisense mRNA; by introducing, controlling or modifying suitable transcriptional activator genes or by introducing an agent which blocks activity level of Gsh1 protein or homolog thereof. Methods of measuring protein levels and protein activity are well known in the art. 
     The modified activity level of the Gsh1 protein or homolog thereof may be reduced, therefore resulting in from 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 95, 96, 97, or 98 to 10, 20, 30, 40, 50, 60, 70, 80, 90, 95, 96, 97, 98 or 99% of the activity level of Gsh1 protein or homolog thereof of a parent or reference fungal host cell, such as a wild-type fungal host cell. The modified, e.g. reduced, activity level of Gsh1 protein or homolog thereof in a fungal host cell may be relative to the activity level of Gsh1 protein or homolog thereof of a reference fungal host cell such as a parent fungal host cell or a wild-type fungal host cell as described above. Consequently, the activity level of Gsh1 protein or homolog thereof in the host cell may be at most 99% of the activity level of Gsh1 protein or homolog thereof in a reference fungal host cell, for example at most 98, 97, 96, 95, 90, 80, 70, 60, 50, 40, 30, 20, or at most 10% of the activity level of Gsh1 protein or homolog thereof in the reference fungal host cell. The activity level of Gsh1 protein or homolog thereof may be reduced to zero or substantially zero. 
     The modified expression level (amount) of Gsh1 protein or homolog thereof may be reduced, therefore resulting in from 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 95, 96, 97, 98 to 10, 20, 30, 40, 50, 60, 70, 80, 90, 95, 96, 97, 98, 99% of the expression level of Gsh1 protein or homolog thereof of the reference fungal host cell, such as a wild-type fungal host cell. The modified, e.g. reduced, expression level of Gsh1 protein or homolog thereof in a fungal host cell may be relative to the expression level of Gsh1 protein or homolog thereof of a reference fungal host cell such as a parent fungal host cell or a wild-type fungal host cell as described above. Consequently, the expression level of Gsh1 protein or homolog thereof in the host cell may be at most 99% of the expression level of Gsh1 protein or homolog thereof in a reference fungal host cell, for example at most 98, 97, 96, 95, 90, 80, 70, 60, 50, 40, 30, 20, or at most 10% of the expression level of Gsh1 protein or homolog thereof in the reference fungal host cell. The expression level of Gsh1 protein or homolog thereof may be reduced to zero or substantially zero. 
     The fungal host cell may lack a functional GSH1 gene or homolog thereof or Gsh1 protein or homolog thereof. For example, the fungal host cell may contain a modified GSH1 gene which may result in a reduced expression level of Gsh1 protein or homolog thereof, or in reduced activity level of Gsh1 protein or homolog thereof. The fungal host cell may lack a GSH1 gene or homolog thereof, for example due to deletion, and/or may lack Gsh1 protein or homolog thereof. 
     GSH1 activity may be measured by using an assay such as that disclosed by Volohonsky et al Chemico-Biological Interactions 140 (2002) 49-65 (incorporated herein by reference), particularly section 2.8.1. Gsh1 expression level may be measured for example by ELISA to determine the amount of protein or by quantitative RT-PCR to measure the RNA level. 
     The fungal host cell may have a modified Gsh1 protein or homolog thereof comprising a mutation at a position corresponding to a position selected from 47, 48, 49, 50, 51, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 409, 451, 452, 453, 454 and 455 of SEQ ID NO: 2, preferably a position selected from: 
     a position corresponding to any of positions 47, 48, 49, 50 and 51 of SEQ ID NO: 2, preferably corresponding to position 49; 
     a position corresponding to any of positions 120, 121, 122, 123, 124, 125, 126, 127, 128, 129 or 130 of SEQ ID NO: 2, preferably corresponding to position 123, 124, 125, 126 or 127, more preferably corresponding to position 125; or 
     a position corresponding to position 409 of SEQ ID NO: 2; 
     a position corresponding to any of positions 451, 452, 453, 454 or 455 of SEQ ID NO: 2, preferably corresponding to position 453. 
     Most preferably, the fungal host cell has a modified Gsh1 protein or homolog thereof comprising a mutation at a position corresponding to position 125 of SEQ ID NO: 2. 
     The mutation may be a substitution, insertion and/or deletion at one or more (e.g. several) positions. Substitutions are preferred. 
     The fungal host cell may comprise a polynucleotide sequence encoding the modified Gsh1 protein or homolog thereof, for example SEQ ID NO: 3. Due to the degeneracy of the genetic code, other polynucleotide sequences can also encode suitable modified Gsh1 proteins or homologs thereof. 
     Amino acids fall into various well-known classes. Therefore, some amino acids are more closely related than others. As used herein, “conservative amino acid substitutions” refers to substitutions made within the same group, and which typically do not substantially affect protein function. By “conservative substitution” is intended within groups such as those shown by  FIG. 1 , this is a Venn diagram which provides one system by which conservation level can be visualized. Generally, substitutions of low conservation are those for which there are many boundaries (lines) between the starting amino acid and the resultant substitution. “Conservative amino acid substitution” includes a substitution made within the same group such as within: 
     aromatic amino acids: F, H, W, Y; 
     aliphatic amino acids: I, L, V; 
     hydrophobic amino acids: A, C, F, H, I, K, L, M, T, V, W, Y; 
     charged amino acids: D, E, H, K, R, for example: 
     positively charged amino acids: H, K, R; or 
     negatively charged amino acids: D, E; 
     polar amino acids: C, D, E, H, K, N, Q, R, S, T, W, Y; 
     small amino acids: A, C, D, G, N, P, S, T, V, for example: 
     tiny amino acids: A, C, G, S. 
     Alternatively, “conservative substitution” may be within the following groups: 
     amino acids having aliphatic side chains: G, A, V, L, I; 
     amino acids having aromatic side chains: F, Y, W; 
     amino acids having sulphur-containing side chains: C, M; 
     amino acids having aliphatic hydroxyl side chains: S, T; 
     amino acids having basic side chains: K, R, H; 
     acidic amino acids and their amide derivatives: D, E, N, Q. 
     Substitutions may be made by techniques known in the art, such as by site-directed mutagenesis as disclosed in U.S. Pat. No. 4,302,386 (incorporated herein by reference). 
     Non-conservative amino substitutions may refer to substitutions made from one group to another group for example from the group having aromatic side chains to the group having aliphatic side chains. 
     The fungal host cell may comprise a modified Gsh1 protein or homolog thereof in which, relative to SEQ ID NO: 2, the mutation is a substitution to an amino acid, preferably a non-conserved amino acid, selected from A, C, D, E, F, G, H, I, K, L, M, N, P, Q, R, S, T, V, W and Y. 
     The mutation at a position corresponding to position 125 of SEQ ID NO: 2 may be a substitution from the native amino acid, such as R, to a non-native amino acid such as to A, C, D, E, F, G, H, I, L, M, N, P, Q, S, T, V, W or Y, preferably to C, D, E or G, more preferably to G. The substitution may be from a positively charged amino acid to an aliphatic, aromatic, hydrophobic, small, tiny, polar or negatively charged amino acid, preferably a negatively charged amino acid to a tiny amino acid. A particularly preferred substitution is from R to G. Substitution to K is less preferred. 
     The mutation at a position corresponding to position 49 of SEQ ID NO: 2 may be a substitution from the native amino acid, such as D, to a non-native amino acid such as A, C, F, G, H, I, K, L, M, N, P, Q, R, S, T, V, W or Y, preferably to H, K or R, more preferably to K or R. The substitution may be from a negatively charged amino acid to a positively charged amino acid. Substitution to E is less preferred. 
     The mutation at a position corresponding to position 409 of SEQ ID NO: 2 may be a substitution from the native amino acid, such as H, to a non-native amino acid such as A, C, D, E, F, G, I, K, L, M, N, P, Q, R, S, T, V, W or Y, preferably to A, I, L, V, M, F, W, Y, more preferably to A, I, L, V, most preferably to L. The substitution may be from an aromatic amino acid to an aliphatic amino acid. A particularly preferred substitution is from H to L. 
     The mutation at a position corresponding to position P453 of SEQ ID NO: 2 may be a substitution from the native amino acid, such as P, to a non-native amino acid such as A, C, D, E, F, G, H, I, K, L, M, N, Q, R, S, T, V, W or Y, preferably to A, I, L, V, M, F, W Y, more preferably to A, I, L, V, most preferably to L. The substitution may be from an aromatic amino acid to an aliphatic amino acid. A particularly preferred substitution is from P to L. 
     A preferred modified Gsh1 protein includes a mutation at a position corresponding to R125 of SEQ ID NO: 2. 
     A preferred modified Gsh1 protein comprises or consists of SEQ ID NO: 4, i.e. which includes the mutation R125G. Such a modified Gsh1 protein may be provided using a nucleotide sequence encoding a Gsh1 protein (e.g. SEQ ID NO: 1), the nucleotide sequence including the single nucleotide polymorphism (SNP) A373G may be provided using, for example SEQ ID NO: 3. 
     Alternatively, the modified level may be an increased level. An increased level or increased activity level of Gsh1 protein or homolog thereof is likely to decrease the yield of desired protein (such as a heterologous protein). Such a decreased yield may be desirable when, for example, the desired protein is detrimental to the viability of the host cell. An increased level may be at least 101, 102, 103, 104, 105, 110, 120, 130, 140, 150, 175, or 200% of the level in a reference host such as a parent host. 
     Position R125 is proposed to be involved in a salt bridge interaction with position D49. Mutation of either amino acid could be used to disrupt this interaction. Mutating R125 to D or E, or D49 to R or K could result in electrostatic repulsion effects which would be expected to destabilise the interaction between positions 125 and 49. However, mutation of R125 to K and/or D49 to E (glutamate) may maintain the interaction. 
     The Gsh1 protein may be exogenous to the host cell or may be endogenous to the host cell. When the Gsh1 protein is exogenous to the host cell, the host cell may maintain or lack a Gsh1 protein that is endogenous to the host cell. 
     The fungal host according to the first aspect of the invention may in addition have:
         a modified Not4 protein or homolog thereof, and/or   a modified level of activity of Not4 protein or homolog thereof, and/or   a modified NOT4 gene or homolog thereof, and/or   a modified level of expression of NOT4 gene or homolog thereof.       

     NOT4 is also known as MOT2. The modified Not4 protein may be modified relative to a reference Not4 protein such as a wild-type Not4 protein, for example SEQ ID NO: 6. Preferably, the modified Not4 protein or homolog thereof has at least 70% identity to SEQ ID NO: 6, more preferably at least 75, 80, 85, 90, 95, 96, 97, 98, 99, 99.1, 99.2, 99.3, 99.4, 99.5, 99.6, 99.7, 99.8 or at least 99.9% identity to SEQ ID NO: 6. The modified Not4 protein or homolog thereof may or may not have at most 99.9, 99.8, 99.7, 99.6, 99.5, 99.4, 99.3, 99.2, 99.1, 99, 98, 97, 96, 95, 90, 85, 80, 75, 70, 65, or at most 60% identity to SEQ ID NO: 6. More preferably, the modified Not4 protein comprises or consists of SEQ ID NO: 8. 
     It is preferred that the modified level of Not4 protein or homolog thereof is a reduced expression level of Not4 protein or homolog thereof or a reduced activity level of Not4 protein or homolog thereof. Preferably the modified, e.g. reduced, level is relative to the level in a reference fungal host cell, such as a fungal host cell in which the Not4 protein comprises or consists of SEQ ID NO: 6. The Not4 protein of the reference fungal host may be a wild-type Not4 sequence, such as SEQ ID NO: 6. A suitable reference fungal host cell is  S. cerevisiae  S288C or  S. cerevisiae  DXY1, as described above. Other suitable reference fungal host cells include cells which are identical to the host cell with the exception of the NOT4 gene or Not4 protein or homolog thereof. For example, the NOT4 gene of the reference may be wild-type (e.g. SEQ ID NO: 5) or the NOT4 gene of the reference may encode wild-type Not4 protein (e.g. SEQ ID NO: 6) or the Not4 protein encoded by the reference may be wild-type (e.g. SEQ ID NO: 6). Preferably, the host cell of the invention is identical to a parent strain with the exception of the NOT4 gene or Not4 protein or homolog thereof. A reference fungal host may also be referred to as a “corresponding” fungal host. A reference fungal host may be a parent fungal host. 
     A reduced level of Not4 protein or activity level of Not4 protein may be achieved, for example, by mutating or deleting the NOT4 gene, thus resulting in a mutated Not4 protein or homolog thereof or complete absence of Not4 protein or homolog thereof; by removing or changing the open reading frame of the gene, by mutating or changing control sequences of the NOT4 gene such as a promoter sequence and/or a terminator sequence; by blocking or reducing transcription of the NOT4 gene for example by introducing suitable interfering RNA such as antisense mRNA, by introducing, controlling or modifying suitable transcriptional activator genes or by introducing an agent which blocks activity level of Not4 protein or homolog thereof. Methods of measuring protein levels are well known in the art. 
     The modified activity level of the Not4 protein or homolog thereof may be reduced, therefore resulting in from 0, 10, 20, 30, 40, 50, 60, 70, 80 or 90 to 10, 20, 30, 40, 50, 60, 70, 80, 90, 95, 96, 97, or 98% of the activity level of Not4 protein or homolog thereof of a parent or reference fungal host cell, such as a wild-type fungal host cell. The modified, e.g. reduced, activity level of Not4 protein or homolog thereof in a fungal host cell may be relative to the activity level of Not4 protein or homolog thereof of a reference fungal host cell such as a parent fungal host cell or a wild-type fungal host cell as described above. Consequently, the activity level of Not4 protein or homolog thereof in the host cell may be at most 99% of the activity level of Not4 protein or homolog thereof in a reference fungal host cell, for example at most 98, 97, 96, 95, 90, 80, 70, 60, 50, 40, 30, 20, or at most 10% of the activity level of Not4 protein or homolog thereof in the reference fungal host cell. The activity level of Not4 protein or homolog thereof may be reduced to zero or substantially zero. 
     The modified expression level (amount) of Not4 protein or homolog thereof may be reduced, therefore resulting in from 0, 10, 20, 30, 40, 50, 60, 70, 80 or 90 to 10, 20, 30, 40, 50, 60, 70, 80, 90, 95, 96, 97, or 98% of the expression level of Not4 protein or homolog thereof of the reference fungal host cell, such as a wild-type fungal host cell. The modified, e.g. reduced, expression level of Not4 protein or homolog thereof in a fungal host cell may be relative to the expression level of Not4 protein or homolog thereof of a reference fungal host cell such as a parent fungal host cell or a wild-type fungal host cell as described above. Consequently, the expression level of Not4 protein or homolog thereof in the host cell may be at most 99% of the expression level of Not4 protein or homolog thereof in a reference fungal host cell, for example at most 98, 97, 96, 95, 90, 80, 70, 60, 50, 40, 30, 20, or at most 10% of the expression level of Not4 protein or homolog thereof in the reference fungal host cell. The expression level of Not4 protein or homolog thereof may be reduced to zero or substantially zero. 
     The fungal host cell may lack a functional NOT4 gene or homolog thereof or Not4 protein or homolog thereof. For example, the fungal host cell may contain a modified NOT4 gene which may result in a reduced expression level of Not4 protein or homolog thereof, or in reduced activity level of Not4 protein or homolog thereof. The fungal host cell may lack a NOT4 gene or homolog thereof, for example due to deletion, and/or may lack Not4 protein or homolog thereof. 
     Not4 expression level may be measured for example by ELISA to determine the amount of protein or by quantitative RT-PCR to measure the RNA level. 
     The modified Not4 protein, or homolog thereof, may be mutated so that its interaction with Nott protein, or homolog thereof, is altered. For example, the N-terminal region of Not4 protein, or homolog thereof, may be mutated, such as the α-helix containing amino acids corresponding to positions 426 to 439 of SEQ ID NO: 6. 
     Therefore, the invention also provides a fungal host cell further having a Not4 protein or homolog thereof which has a weaker interaction, such as hydrophobic interaction, with Nott than the interaction between a wild-type Not4 protein (e.g. SEQ ID NO: 6) and a wild-type Nott protein (e.g. SEQ ID NO: 13). 
     The fungal host cell may have a modified Not4 protein or homolog thereof comprising a mutation at a position corresponding to a position selected from 426, 427, 428, 429, 430, 431, 432, 433, 434, 435, 436, 437, 438, 439, 440, 441, 442, 443, 444, 445, 446, 447, 448, 449, 450, 451, 452, 453, 454, 455, 456, 457, 458, 459, 460, 461, 462, 463, 464, 465, 466, 467, 468, 469 or 470 of SEQ ID NO: 6, preferably a position selected from: 
     a position corresponding to 426, 427, 428, 429, 430, 431, 432, 433, 434, 435, 436, 437, 438, or 439 of SEQ ID NO: 6, preferably position 429, 430, 434, or 437, most preferably position 429; 
     a position corresponding to 460, 461, 462, 463, 464, 465, 466, 467, 468, 469 or 470 of SEQ ID NO: 6, preferably position 463, 464, or 466; or a position corresponding to 438, 439, 440, 441, 442, 443, 444, 445, 446, 447, 448, 449, 450, 451, 452, 453, 454, 455, or 456 of SEQ ID NO: 6, preferably position 442, 445, 447 or 452. 
     The mutation may be a substitution, insertion and/or deletion at one or more (e.g. several) positions. Substitutions are preferred. 
     The fungal host cell may comprise a polynucleotide sequence encoding the modified Not4 protein or homolog thereof, for example SEQ ID NO: 7. Due to the degeneracy of the genetic code, other polynucleotide sequences can also encode suitable modified Not4 proteins or homologs thereof. 
     The fungal host cell may comprise a modified Not4 protein or homolog thereof in which, relative to SEQ ID NO: 6, the mutation is a substitution to an amino acid, preferably a non-conserved amino acid, selected from A, C, D, E, F, G, H, I, K, L, M, N, P, Q, R, S, T, V, W and Y. 
     The mutation at a position corresponding to position 429 of SEQ ID NO: 6 may be a substitution from the native amino acid, such as F, to a non-native amino acid such as A, C, D, E, F, G, H, I, K, L, M, N, P, Q, R, S, T, V, W, or Y, preferably to G, A, V, L, or I, more preferably to V, L or I, most preferably to I. The substitution may be to a non-conserved amino acid. The substitution may be to an aliphatic amino acid. A particularly preferred substitution is from F to I. 
     The mutation at a position corresponding to position 430 of SEQ ID NO: 6 may be a substitution from the native amino acid, such as L, to any non-native amino acid such as A, C, D, E, F, G, H, I, K, L, M, N, P, Q, R, S, T, V, W, or Y. The substitution may be to a non-conserved amino acid. 
     The mutation at a position corresponding to position 434 may be a substitution from the native amino acid, such as L, to any non-native amino acid such as A, C, D, E, F, G, H, I, K, L, M, N, P, Q, R, S, T, V, W, or Y. The substitution may be to a non-conserved amino acid. 
     The mutation at a position corresponding to position 437 of SEQ ID NO: 6 may be a substitution from the native amino acid, such as L, to any non-native amino acid such as A, C, D, E, F, G, H, I, K, L, M, N, P, Q, R, S, T, V, W, or Y. The substitution may be to a non-conserved amino acid. 
     A preferred modified Not4 protein includes a mutation at a position corresponding to F429 of SEQ ID NO: 6. 
     A preferred modified Not4 protein comprises or consists of SEQ ID NO: 8, i.e. which includes the mutation F4291. Such a modified Not4 protein may be provided using a nucleotide sequence encoding a Not4 protein (e.g. SEQ ID NO: 5), the nucleotide sequence including the SNP T1285A, for example SEQ ID NO: 7. 
     Alternatively, the modified level may be increased. An increased level or increased activity of Not4 protein or homolog thereof is likely to decrease the yield of desired protein (such as a heterologous protein). Such a decreased yield may be desirable when, for example, the desired protein is detrimental to the viability of the host cell. An increased level may be at least 101, 102, 103, 104, 105, 110, 120, 130, 140, 150, 175, or 200% of the level in a reference host such as a parent host. 
     The Not4 protein may be exogenous to the host cell or may be endogenous to the host cell. When the Not4 protein is exogenous to the host cell, the host cell may maintain or lack a Not4 protein that is endogenous to the host cell. 
     The fungal host may have both (1) a modified level of Gsh1 protein or homolog thereof and/or a modified level of activity of Gsh1 protein or homolog thereof, and/or a modified GSH1 gene or homolog thereof, and/or a modified level of expression of GSH1 gene or homolog thereof and (2) a modified level of Not4 protein or homolog thereof and/a modified level of activity of Not4 protein or homolog thereof, and/or a modified NOT4 gene or homolog thereof, and/or a modified level of expression of NOT4 gene or homolog thereof. Preferably, the fungal host has (1) a reduced level of Gsh1 protein or homolog thereof or reduced level of activity of Gsh1 protein or homolog thereof and/or a reduced level of expression of GSH1 gene or homolog thereof and (2) a reduced level of Not4 protein or homolog thereof or reduced level of activity of Not4 protein or homolog thereof and/or a reduced level of expression of NOT4 gene or homolog thereof. Alternatively, the fungal host may have (1) a reduced level of Gsh1 protein or homolog thereof or reduced level of activity of Gsh1 protein or homolog thereof and/or a reduced level of expression of GSH1 gene or homolog thereof and (2) an increased level of Not4 protein or homolog thereof or increased level of activity of Not4 protein or homolog thereof and/or an increased level of expression of NOT4 gene or homolog thereof. Alternatively, the fungal host may have (1) an increased level of Gsh1 protein or homolog thereof or increased level of activity of Gsh1 protein or homolog thereof and/or an increased level of expression of GSH1 gene or homolog thereof and (2) a reduced level of Not4 protein or homolog thereof or reduced level of activity of Not4 protein or homolog thereof and/or a reduced level of expression of NOT4 gene or homolog thereof. The same options apply with respect to expression levels of GSH1 and NOT4. ‘Increased’ and ‘reduced’ are as described herein. 
     Preferably the modified, e.g. reduced, level of Gsh1 is relative to the level in a reference fungal host cell, such as a fungal host cell in which the Gsh1 protein comprises or consists of SEQ ID NO: 2 and the modified e.g. reduced, level of Not4 is relative to the level in a reference fungal host cell, such as a fungal host cell in which the Not4 protein comprises or consists of SEQ ID NO: 6. The Gsh1 protein of the reference fungal host may be a wild-type Gsh1 sequence, such as SEQ ID NO: 2. The Not4 protein of the reference fungal host may be a wild-type Not4 sequence, such as SEQ ID NO: 6. A suitable reference fungal host cell is  S. cerevisiae  S288C or  S. cerevisiae  DXY1 as described above. Other suitable reference fungal host cells include cells which are identical to the host cell with the exception of the GSH1 gene or Gsh1 protein or homolog thereof and the NOT4 gene or Not4 protein or homolog thereof. For example, the GSH1 gene of the reference may be wild-type (e.g. SEQ ID NO: 1) or the GSH1 gene of the reference may encode wild-type Gsh1 protein (e.g. SEQ ID NO: 2) or the Gsh1 protein encoded by the reference may be wild-type (e.g. SEQ ID NO: 2). The NOT4 gene of the reference may be wild-type (e.g. SEQ ID NO: 5) or the NOT4 gene of the reference may encode wild-type Not4 protein (e.g. SEQ ID NO: 6) or the Not4 protein encoded by the reference may be wild-type (e.g. SEQ ID NO: 6). Preferably, the host cell of the invention is identical to a parent strain with the exception of the GSH1 gene or Gsh1 protein or homolog thereof and the NOT4 gene or Not4 protein or homolog thereof. A reference fungal host may also be referred to as a “corresponding” fungal host. A reference fungal host may be a parent fungal host. 
     The fungal host cell may be a recombinant fungal host cell. 
     The fungal host cell may be a yeast or a filamentous fungus. “Fungi” as used herein includes the phyla Ascomycota, Basidiomycota, Chytridiomycota, and Zygomycota (as defined by Hawksworth et al., in,  Ainsworth and Bisby&#39;s Dictionary of The Fungi,  8th edition, 1995, CAB International, University Press, Cambridge, UK) as well as the Oomycota (as cited in Hawksworth et al., 1995, supra, page 171) and all mitosporic fungi (Hawksworth et al., 1995, supra). 
     In a preferred aspect, the fungal host cell is a yeast cell. “Yeast” as used herein includes ascosporogenous yeast (Endomycetales), basidiosporogenous yeast, and yeast belonging to the Fungi Imperfecti (Blastomycetes). Since the classification of yeast may change in the future, for the purposes of this invention, yeast shall be defined as described in  Biology and Activities of Yeast  (Skinner, F. A., Passmore, S. M., and Davenport, R. R., eds,  Soc. App. Bacteriol. Symposium Series  No: 9, 1980, pages 1 to 27). 
     In a more preferred aspect, the yeast host cell is a  Candida, Hansenula, Kluyveromyces, Pichia, Saccharomyces, Schizosaccharomyces , or  Yarrowia  cell. 
     In a more preferred aspect, the yeast host cell is a  Saccharomyces carlsbergensis, Saccharomyces cerevisiae, Saccharomyces diastaticus, Saccharomyces douglasii, Saccharomyces kluyveri, Saccharomyces norbensis, Saccharomyces oviformis, Kluyveromyces lactis  or a  Yarrowia lipolytica  cell. A  Saccharomyces cerevisiae  host is particularly preferred. 
     The  S. cerevisiae  host may or may not comprise one or more of the following genotypic features: leu2-3, leu2-122, can1, pra1, ubc4, ura3, yap3::URA3, lys2, hsp150::LYS2, pmt1::URA3 (as defined in WO2014/138371, incorporated herein by reference), for example  S. cerevisiae  BXP10. Preferably the  S. cerevisiae  host includes MATa. 
     The  S. cerevisiae  host may or may not comprise one or more of the following genotype, MATa, leu2-3, leu2-112, ubc4, ura3, yap3::URA3, lys2, hsp150::LYS2; with PDI1, URA3 and Ylplac211 integrated at the PDI1 locus (Finnis et al 2010, Microbial Cell Factories 9:87), for example  S. cerevisiae  DP9. 
     The  S. cerevisiae  host may or may not comprise one or more of the following genotype, MATα, leu2, pep4-3, for example  S. cerevisiae  MT302/28B as described in Finnis et al 1993, Eur. J. Biochem, 212: 201-210. 
     The  S. cerevisiae  host may or may not comprise the following genotype: MATα, SUC2, gal2, mal2, mel, flo1, flo8-1, hap1, ho, bio1, bio6 (Mortimer and Johnston (1986) Genetics 113:35-43), for example  S. cerevisiae  S288C. 
     A preferred  S. cerevisiae  host strain comprises or consists of all of MATa, leu2-3, leu2-122, can1, pra1, ubc4, ura3, yap3::URA3, lys2, hsp150::LYS2, and pmt1::URA3. 
     Another preferred  S. cerevisiae  host comprises or consists of all of: MATa, leu2-3, leu2-112, ubc4, ura3, yap3::URA3, lys2, hsp150::LYS2, with PDI1, URA3 and Ylplac211 integrated at the PDI1 locus. 
     Another preferred  S. cerevisiae  host comprises or consists of all of: MATa, SUC2, gal2, mal2, mel, flo1, flo8-1, hap1, ho, bio1, bio6. 
     Another preferred  S. cerevisiae  host comprises or consists of all of: MATα, leu2, pep4-3. 
     The host may be polyploid, diploid or halpoid. A haploid or diploid yeast host is preferred, preferably haploid. 
     The host mating type may be, for example, MATa or MATα (Mat-alpha). Preferably the  S. cerevisiae  host contains a plasmid encoding human albumin or variant, fragment and/or fusion thereof. 
     “Filamentous fungi” include all filamentous forms of the subdivision Eumycota and Oomycota (as defined by Hawksworth et al., 1995, supra). The filamentous fungi are characterized by a mycelial wall composed of chitin, cellulose, glucan, chitosan, mannan, and other complex polysaccharides. Vegetative growth is by hyphal elongation and carbon catabolism is obligately aerobic. In contrast, vegetative growth by yeasts such as  Saccharomyces cerevisiae  is by budding of a unicellular thallus and carbon catabolism may be fermentative. 
     Preferred filamentous fungal host cells may or may not include  Acremonium, Aspergillus, Aureobasidium, Bjerkandera, Ceriporiopsis, Chrysosporium, Coprinus, Coriolus, Cryptococcus, Filibasidium, Fusarium, Humicola, Magnaporthe, Mucor, Myceliophthora, Neocallimastix, Neurospora, Paecilomyces, Penicillium, Phanerochaete, Phlebia, Piromyces, Pleurotus, Schizophyllum, Talaromyces, Thermoascus, Thielavia, Tolypocladium, Trametes  or  Trichoderma.    
     The fungal host cell, may comprise a nucleotide sequence encoding a desired protein. Preferably, the desired protein is a heterologous protein. A heterologous protein is one not naturally produced by the host cell and, preferably, does not include proteins such as selectable markers, for example antibiotic resistance markers or auxotrophic markers, chaperones, FLP or FRT. 
     The fungal host cell may be an expression host. The fungal host cell may comprise an expression cassette for example encoding a desired protein such as a heterologous protein. The expression cassette may be, for example within a vector such as a plasmid. The fungal host cell may comprise an expression vector. 
     The desired protein may or may not be a plant or animal protein or variant thereof. The desired protein may, or may not, comprise the sequence of albumin, a monoclonal antibody, an etoposide, a serum protein (such as a blood clotting factor), antistasin, a tick anticoagulant peptide, transferrin, lactoferrin, endostatin, angiostatin, collagens, immunoglobulins or immunoglobulin-based molecules or fragment of either (e.g. a Small Modular ImmunoPharmaceutical™ (“SMIP”) or dAb, Fab′ fragments, F(ab′)2, scAb, scFv or scFv fragment), a Kunitz domain protein (such as those described in WO03/066824 (incorporated herein by reference), with or without albumin fusions), interferons, interleukins, IL-10, IL-11, IL-2, interferon α (alpha) species and sub-species, interferon β (beta) species and sub-species, interferon γ (gamma) species and sub-species, leptin, CNTF, CNTF Ax15 , IL-1-receptor antagonist, erythropoietin (EPO) and EPO mimics, thrombopoietin (TPO) and TPO mimics, prosaptide, cyanovirin-N, 5-helix, T20 peptide, T1249 peptide, HIV gp41, HIV gp120, urokinase, prourokinase, tPA, hirudin, platelet derived growth factor, parathyroid hormone, proinsulin, insulin, glucagon, glucagon-like peptides such as exendin-4, GLP-1 or GLP-2, insulin-like growth factor, calcitonin, growth hormone, transforming growth factor β (beta), tumour necrosis factor, G-CSF, GM-CSF, M-CSF, FGF, coagulation factors in both pre and active forms, including but not limited to plasminogen, fibrinogen, thrombin, pre-thrombin, pro-thrombin, von Willebrand&#39;s factor, alpha 1 -antitrypsin, plasminogen activators, Factor VII, Factor VIII, Factor IX, Factor X and Factor XIII, nerve growth factor, LACI, platelet-derived endothelial cell growth factor (PD-ECGF), glucose oxidase, serum cholinesterase, aprotinin, amyloid precursor protein, inter-alpha trypsin inhibitor, antithrombin III, apo-lipoprotein species, Protein C, Protein S, a metabolite, an antibiotic, or a variant or fragment of any of the above. 
     Preferably the variant has at least 70, 75, 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99% identity to one or more of the proteins disclosed above. 
     A preferred desired protein may or may not be a serum protein such as an albumin or variant, fragment and/or fusion thereof. Preferably, the albumin has from 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, 98.2, 98.4, 98.6, 98.8, 99, 99.2, 99.3, 99.4, 99.5, 99.6, 99.7, 99.8, or 99.9 to 70, 75, 80, 85, 90, 95, 96, 97, 98, 98.2, 98.4, 98.6, 98.8, 99, 99.2, 99.3, 99.4, 99.5, 99.6, 99.7, 99.8, 99.9, or 100% sequence identity to SEQ ID NO: 10. Most preferably, the albumin comprises or consists of SEQ ID NO: 10. 
     The albumin variant, fragment and/or fusion thereof may or may not comprise from 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, or 19 to 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 mutations relative to SEQ ID NO: 10. Preferred albumin variants comprises from 1 to 10 mutations relative to SEQ ID NO: 10, more preferably from 1 to 5 mutations. Preferred mutations include substitutions. 
     The albumin variant, fragment and/or fusion thereof may or may not comprise A, C, D, E, F, G, H, I, L, M, N, P, Q, R, S, T, V, W or Y at a position corresponding to position K573 of SEQ ID NO: 10, more preferably a P, H, W or Y at a position corresponding to position K573 of SEQ ID NO: 10. Particularly preferred albumin variants have at least 95% identity to SEQ ID NO: 10 (more preferably at least 96, 97, 98 or 99% identity) and comprise P at a position corresponding to 573 of SEQ ID NO: 10. 
     The albumin variant, fragment and/or fusion thereof may or may not comprise A, C, D, F, G, H, I, K, L, M, N, P, Q, R, S, T, V, W or Y at a position corresponding to position E492 of SEQ ID NO: 10, more preferably a G, D, F, H, M or R at a position corresponding to position E492 of SEQ ID NO: 10, even more preferably a G or D at a position corresponding to position E492 of SEQ ID NO: 10. Particularly preferred albumin variants have at least 95% identity to SEQ ID NO: 10 (more preferably at least 96, 97, 98 or 99% identity) and comprise G at a position corresponding to E492 of SEQ ID NO: 10. 
     The albumin variant, fragment and/or fusion thereof may or may not comprise A, C, D, E, F, G, H, I, L, M, N, P, Q, R, S, T, V, W or Y at a position corresponding to position K574 of SEQ ID NO: 10, more preferably a H, G, D, F, N, S or Y at a position corresponding to position K574 of SEQ ID NO: 10, even more preferably a D, F, G or H at a position corresponding to position K574 of SEQ ID NO: 10. Particularly preferred albumin variants have at least 95% identity to SEQ ID NO: 10 (more preferably at least 96, 97, 98 or 99% identity) and comprise H at a position corresponding to K574 of SEQ ID NO: 10. 
     The albumin variant, fragment and/or fusion thereof may or may not comprise A, C, D, E, F, G, H, I, K, L, M, N, P, R, S, T, V, W or Y at a position corresponding to position Q580 of SEQ ID NO: 10, more preferably a K or R at a position corresponding to position Q580 of SEQ ID NO: 10. Particularly preferred albumin variants have at least 95% identity to SEQ ID NO: 10 (more preferably at least 96, 97, 98 or 99% identity) and comprise K at a position corresponding to Q580 of SEQ ID NO: 10. 
     Preferred albumin variants may or may not comprise mutations at one or more positions selected to those corresponding to positions 492, 573, 574 and 580, for example the substitutions described above. For example, the albumin variant may comprise or consist of SEQ ID NO: 45. 
     Other preferred albumin variants, fragments and/or fusions thereof include those disclosed in WO2011/051489, WO2011/124718, WO2012/059486, WO2012/150319, WO2014/072481, WO2013/135896, WO2015/036579, WO2010/092135, WO2013/075066, WO2014/179657, WO2009/126920, WO2010/059315, WO2011/103076, WO2012/112188, WO2015/063611 and WO 2017/029407 or fragments of fusions thereof (each incorporated herein by reference). 
     The albumin may or may not be a fragment of an albumin or variant thereof. 
     The albumin variant, fragment and/or fusion thereof may have a binding affinity to FcRn that is stronger or weaker (and, preferably, is stronger) than that of the parent albumin, fragment and/or fusion thereof. 
     The albumin variant, fragment and/or fusion thereof may have a KD to FcRn (e.g. shFcRn) that is lower than the corresponding KD for HSA or conjugate thereof to. Preferably, the KD for the albumin variant, fragment and/or fusion thereof is less than 0.9×KD for HSA to FcRn, more preferred less than 0.5×KD for HSA to FcRn, more preferred less than 0.1×KD for HSA to FcRn, even more preferred less than 0.05×KD for HSA to FcRn, even more preferred less than 0.02×KD for HSA to FcRn, even more preferred less than 0.01×KD for HSA to FcRn and most preferred less than 0.001×KD for HSA to FcRn (where × means ‘multiplied by’). A lower KD corresponds to a stronger binding affinity. 
     The albumin variant, fragment and/or fusion thereof may have a KD to FcRn that is higher than the corresponding KD for HSA or conjugate thereof to FcRn. Preferably, the KD for the albumin variant, fragment and/or fusion thereof is more than 2×KD for HSA to FcRn, more preferred more than 5×KD for HSA to FcRn, more preferred more than 10×KD for HSA to FcRn, even more preferred more than 25×KD for HSA to FcRn, most preferred more than 50×KD for HSA to FcRn. The albumin variant, fragment and/or fusion thereof may be a null binder to FcRn. A higher KD corresponds to a weaker binding affinity. 
     When determining and/or comparing KD, one or more (e.g. several) (and preferably all) of the following parameters may be used: 
     Instrument: Biacore 3000 instrument (GE Healthcare) 
     Flow cell: CM5 sensor chip 
     FcRn: human FcRn, preferably soluble human FcRn, optionally coupled to a tag such as Glutathione S Transferase (GST) or Histidine (His), most preferably His such as 6 histidine residues at the C-terminus of the beta-2-microglobulin. 
     Quantity of FcRn: 1200-2500 RU 
     Coupling chemistry: amine coupling chemistry (e.g. as described in the protocol provided by the manufacturer of the instrument). 
     Coupling method: The coupling may be performed by injecting 20 μg/ml of the protein in 10 mM sodium acetate pH 5.0 (GE Healthcare). Phosphate buffer (67 mM phosphate buffer, 0.15 M NaCl, 0.005% Tween 20) at pH 5.5 may be used as running buffer and dilution buffer. Regeneration of the surfaces may be done using injections of HBS-EP buffer (0.01 M HEPES, 0.15 M NaCl, 3 mM EDTA, 0.005% surfactant P20) at pH 7.4 (Biacore AB). 
     Quantity of injection of test molecule (e.g. HSA or variant) 20-0.032 μM. 
     Flow rate of injection: constant, e.g. 30 μl/ml. 
     Temperature of injection: 25° C. 
     Data evaluation software: BIAevaluation 4.1 software (BIAcore AB). 
     The albumin variant, fragment and/or fusion thereof may have a plasma half-life that is longer or shorter, preferably longer, than that of the parent albumin, fragment and/or fusion thereof. 
     Plasma half-life is ideally determined in vivo in suitable individuals. However, since it is time consuming and expensive and inevitably there are ethical concerns connected with doing experiments in animals or man, it is desirable to use an in vitro assay for determining whether plasma half-life is extended or reduced. It is known that the binding of albumin to its receptor (FcRn) is important for plasma half-life and the correlation between receptor binding and plasma half-life is that a higher affinity of albumin to its receptor leads to longer plasma half-life. Thus, for the invention, a higher affinity of albumin to FcRn is considered indicative of an increased plasma half-life and a lower affinity of albumin to its receptor is considered indicative of a reduced plasma half-life. 
     The binding of albumin to its receptor FcRn may be described using the term affinity and the expressions “stronger” or “weaker”. Thus, it should be understood that, a molecule having a higher affinity to FcRn than the affinity of HSA to FcRn is considered to bind more strongly to FcRn than HSA binds to FcRn and a molecule having a lower affinity to FcRn than the affinity of HSA to FcRn is considered to bind more weakly to FcRn than HSA binds to FcRn. The term ‘binding coefficient’ can be used instead of the term ‘binding affinity’. 
     The terms “longer plasma half-life” or “shorter plasma half-life” and similar expressions are understood to be in relationship to the corresponding parent or reference or corresponding albumin molecule. Thus, a longer plasma half-life with respect to a variant albumin of the invention means that the variant has longer plasma half-life than that of the corresponding albumin having the same sequences except for the alteration(s) described herein. 
     The albumin or variant, and/or fragment thereof may or may not be genetically fused to a fusion partner. Preferably, the fusion partner is a non-albumin protein. The fusion partner may be fused at the N′ or C′ terminus of the albumin. There may or may not be one or more spacer amino acids located between the albumin moiety and the partner moiety. Fusion partners may be inserted within the albumin sequence. The fusion partner may be at least 5 amino acids long, for example at least 5, 10, 15, 20, 25, 30, 35, 40, 50, 60, 70, 80, 90 or at least 100 amino acids long. The fusion partner may or may not have a maximum length of from 35, 30, 40, 50, 60, 70, 80, 90, 100, 125, 150, 175, 200, 300, 400, 500, 600, 700, 800, 900 or 1000 amino acids long. The fusion protein may comprise one or more fusion partners, for example fused at the N′ or C′ terminus of albumin or inserted within the albumin sequence. The fusion protein may comprise one or more (e.g. several, such as 2, 3, 4 or 5) copies of the same fusion partner or two or more different partners. The fusion partner may be selected from desired or heterologous proteins as disclosed above. 
     A preferred fusion protein may comprise a polypeptide having GLP-1 activity such as those described in WO2014/138371 (incorporated herein by reference, with particular reference to pages 13, 14, 26, 34 to 37). For example, a preferred fusion protein may comprise HSA (SEQ ID NO: 10), or a variant (for example SEQ ID NO: 45) and/or fragment of HSA genetically fused in series to one copy of a GLP analog (e.g. SEQ ID NO: 14 or 51) or HSA (SEQ ID NO: 10), or a variant (for example SEQ ID NO: 45) and/or fragment of HSA genetically fused in series to a tandem repeat of a GLP analog (e.g. SEQ ID NO: 15, 52 or 53). For example, the fusion protein may comprise or consist of SEQ ID NO: 16 (albiglutide). 
     Particularly suitable fungal host cells for the production of albumins, variants, fragments and/or fusions thereof include, but are not limited to,  Aspergillus  (WO06/066595),  Kluyveromyces  (Fleer, 1991, Bio/technology 9: 968-975),  Pichia  (Kobayashi, 1998, Therapeutic Apheresis 2: 257-262) and  Saccharomyces  (Sleep, 1990, Bio/technology 8: 42-46)), each incorporated herein by reference. 
     The desired protein (such as a heterologous protein) may or may not be a secreted protein. Therefore, the protein encoded by the host cell may or may not comprise a signal peptide (which in some literature may also be referred to as a “leader sequence”). Typically, the signal peptide sequence is cleaved from the protein during secretion from the host cell, therefore the resultant (mature) protein does not comprise a signal peptide sequence. Examples of suitable signal peptide sequences are provided below. A signal peptide may or may not comprise a pro-peptide. 
     Alternatively, the desired protein may or may not be intracellular. 
     The desired protein may or may not be encoded by a plasmid. 
     The desired protein may or may not be encoded by chromosomal nucleic acid. 
     Suitable plasmids include 2-micron family plasmids such as those described in WO2006/067511 (incorporated herein by reference, with particular emphasis on the section titled “The 2 μm-family plasmids:” on pages 46 to 61). Such plasmids, collectively termed “2 μm-family plasmids”, include pSR1, pSB3 and pSB4 from  Zygosaccharomyces rouxii  (formerly classified as  Zygosaccharomyces bisporus ), plasmids pSB1 and pSB2 from  Zygosaccharomyces bailii , plasmid pSM1 from  Zygosaccharomyces fermentati , plasmid pKD1 from  Kluyveromyces drosphilarum , an un-named plasmid from  Pichia membranaefaciens  (“pPM1”) and the 2 μm plasmid (such as shown in FIG. 1 of WO2006/067511) and variants (such as Scp1, Scp2 and Scp3) from  Saccharomyces cerevisiae  (Volkert, et al., 1989 , Microbiological Reviews  53: 299; Murray et al., 1988 , J. Mol. Biol.  200: 601; Painting, et al., 1984 , J. Applied Bacteriology  56: 331). 
     A 2 μm-family plasmid typically comprises at least three open reading frames (“ORFs”) that each encodes a protein that functions in the stable maintenance of the 2 μm-family plasmid as a multicopy plasmid. The proteins encoded by the three ORFs can be designated FLP, REP1 and REP2. Where a 2 μm-family plasmid comprises not all three of the ORFs encoding FLP, REP1 and REP2 then ORFs encoding the missing protein(s) should be supplied in trans, either on another plasmid or by chromosomal integration. 
     A preferred plasmid is the 2 μm plasmid from  S. cerevisiae , preferably encoding a desired protein such as a heterologous protein. 
     The Gsh1 protein, Not4 protein and/or the desired, e.g. heterologous, protein may be encoded by a nucleotide sequence operably linked to one or more control sequences that direct the expression of the coding sequence in a suitable host cell under conditions compatible with the control sequences. 
     The polynucleotide may be manipulated in a variety of ways to provide for expression of a polypeptide. Manipulation of the polynucleotide prior to its insertion into a vector may be desirable or necessary depending on the expression vector. The techniques for modifying polynucleotides utilizing recombinant DNA methods are known in the art. 
     The control sequence may be a promoter, a polynucleotide which is recognized by a host cell for expression of the polynucleotide. The promoter contains transcriptional control sequences that mediate the expression of the polypeptide. The promoter may be any polynucleotide that shows transcriptional activity in the host cell including mutant, truncated, and hybrid promoters, and may be obtained from genes encoding extracellular or intracellular polypeptides either homologous or heterologous to the host cell. 
     Examples of suitable promoters for directing transcription of the nucleic acid constructs of the present invention in a filamentous fungal host cell are promoters obtained from the genes for  Aspergillus nidulans  acetamidase,  Aspergillus niger  neutral alpha-amylase,  Aspergillus niger  acid stable alpha-amylase,  Aspergillus niger  or  Aspergillus awamori  glucoamylase (glaA),  Aspergillus oryzae  TAKA amylase,  Aspergillus oryzae  alkaline protease,  Aspergillus oryzae  triose phosphate isomerase,  Fusarium oxysporum  trypsin-like protease (WO96/00787),  Fusarium venenatum  amyloglucosidase (WO00/56900),  Fusarium venenatum  Daria (WO00/56900),  Fusarium venenatum  Quinn (WO00/56900),  Rhizomucor miehei  lipase,  Rhizomucor miehei  aspartic proteinase,  Trichoderma reesei  beta-glucosidase,  Trichoderma reesei  cellobiohydrolase I,  Trichoderma reesei  cellobiohydrolase II,  Trichoderma reesei  endoglucanase I,  Trichoderma reesei  endoglucanase II,  Trichoderma reesei  endoglucanase III,  Trichoderma reesei  endoglucanase IV,  Trichoderma reesei  endoglucanase V,  Trichoderma reesei  xylanase I,  Trichoderma reesei  xylanase II,  Trichoderma reesei  beta-xylosidase, as well as the NA2-tpi promoter (a modified promoter from an  Aspergillus  neutral alpha-amylase gene in which the untranslated leader has been replaced by an untranslated leader from an  Aspergillus  triose phosphate isomerase gene; non-limiting examples include modified promoters from an  Aspergillus niger  neutral alpha-amylase gene in which the untranslated leader has been replaced by an untranslated leader from an  Aspergillus nidulans  or  Aspergillus oryzae  triose phosphate isomerase gene); and mutant, truncated, and hybrid promoters thereof. 
     In a yeast host, useful promoters are obtained from the genes for  Saccharomyces cerevisiae  enolase (ENO1),  Saccharomyces cerevisiae  galactokinase (GAL1),  Saccharomyces cerevisiae  alcohol dehydrogenase/glyceraldehyde-3-phosphate dehydrogenase (ADH1, ADH2/GAP),  Saccharomyces cerevisiae  triose phosphate isomerase (TPI),  Saccharomyces cerevisiae  metallothionein (CUP1), and  Saccharomyces cerevisiae  3-phosphoglycerate kinase. Other useful promoters for yeast host cells are described by Romanos et al., 1992, supra. 
     The control sequence may also be a transcription terminator, which is recognized by a host cell to terminate transcription. The terminator sequence is operably linked to the 3′-terminus of the polynucleotide encoding the polypeptide. Any terminator that is functional in the host cell may be used. 
     Preferred terminators for filamentous fungal host cells are obtained from the genes for  Aspergillus nidulans  anthranilate synthase,  Aspergillus niger  glucoamylase,  Aspergillus niger  alpha-glucosidase,  Aspergillus oryzae  TAKA amylase, and  Fusarium oxysporum  trypsin-like protease. 
     Preferred terminators for yeast host cells are obtained from the genes for  Saccharomyces cerevisiae  enolase,  Saccharomyces cerevisiae  cytochrome C (CYC1), and  Saccharomyces cerevisiae  glyceraldehyde-3-phosphate dehydrogenase. Other useful terminators for yeast host cells are described by Romanos et al., 1992, supra. 
     The control sequence may also be an mRNA stabilizer region downstream of a promoter and upstream of the coding sequence of a gene which increases expression of the gene. 
     The control sequence may also be a leader, a nontranslated region of an mRNA that is important for translation by the host cell. The leader sequence is operably linked to the 5′-terminus of the polynucleotide encoding the polypeptide. Any leader that is functional in the host cell may be used. 
     Preferred leaders for filamentous fungal host cells are obtained from the genes for  Aspergillus oryzae  TAKA amylase and  Aspergillus nidulans  triose phosphate isomerase. 
     Suitable leaders for yeast host cells are obtained from the genes for  Saccharomyces cerevisiae  enolase (ENO-1),  Saccharomyces cerevisiae  3-phosphoglycerate kinase,  Saccharomyces cerevisiae  alpha-factor, and  Saccharomyces cerevisiae  alcohol dehydrogenase/glyceraldehyde-3-phosphate dehydrogenase (ADH2/GAP). 
     The control sequence may also be a polyadenylation sequence, a sequence operably linked to the 3′-terminus of the polypeptide-encoding sequence and, when transcribed, is recognized by the host cell as a signal to add polyadenosine residues to transcribed mRNA. Any polyadenylation sequence that is functional in the host cell may be used. 
     Preferred polyadenylation sequences for filamentous fungal host cells are obtained from the genes for  Aspergillus nidulans  anthranilate synthase,  Aspergillus niger  glucoamylase,  Aspergillus niger  alpha-glucosidase,  Aspergillus oryzae  TAKA amylase, and  Fusarium oxysporum  trypsin-like protease. 
     Useful polyadenylation sequences for yeast host cells are described by Guo and Sherman, 1995 , Mol. Cellular Biol.  15: 5983-5990. 
     The control sequence may also be a signal peptide coding region that encodes a signal peptide linked to the N-terminus of a polypeptide and directs the polypeptide into the cell&#39;s secretory pathway. The 5′-end of the coding sequence of the polynucleotide may inherently contain a signal peptide coding sequence naturally linked in translation reading frame with the segment of the coding sequence that encodes the polypeptide. Alternatively, the 5′-end of the coding sequence may contain a signal peptide coding sequence that is foreign to the coding sequence. A foreign signal peptide coding sequence may be required where the coding sequence does not naturally contain a signal peptide coding sequence. Alternatively, a foreign signal peptide coding sequence may simply replace the natural signal peptide coding sequence in order to enhance secretion of the polypeptide. However, any signal peptide coding sequence that directs the expressed polypeptide into the secretory pathway of a host cell may be used. 
     Effective signal peptide coding sequences for filamentous fungal host cells are the signal peptide coding sequences obtained from the genes for  Aspergillus niger  neutral amylase,  Aspergillus niger  glucoamylase,  Aspergillus oryzae  TAKA amylase,  Humicola insolens  cellulase,  Humicola insolens  endoglucanase V,  Humicola lanuginosa  lipase, and  Rhizomucor miehei  aspartic proteinase. 
     Preferred signal peptides for yeast host cells, for example yeast host cells for the production of albumin, or variant, fragment and/or fusion thereof, include: 
     a signal peptide obtained from the gene for  Saccharomyces cerevisiae  alpha-factor, 
     a signal peptide obtained from the gene for  Saccharomyces cerevisiae  invertase, 
     a signal peptide obtained from the gene for  Saccharomyces cerevisiae  KEX2 e.g. comprising or consisting of SEQ ID NO: 17 or a modified KEX2 signal peptide sequence e.g. comprising or consisting of SEQ ID NO: 18. 
     Particularly preferred signal peptides include: 
     a signal peptide comprising a fusion of the mating factor alpha signal peptide sequence and the human albumin signal peptide sequence as taught in WO90/01063 (incorporated herein by reference), an example of such a signal peptide sequence is provided in SEQ ID NO: 19; 
     a signal peptide comprising the pentapeptide motif of SEQ ID NO: 20, wherein the pentapeptide motif is located in the hydrophobic domain of the signal peptide sequence, for example from positions −10 to −25 of an immature protein, where position −1 refers to the amino acid of the signal peptide sequence which is immediately adjacent the N-terminus of the first amino acid of the mature sequence, or for signal peptide sequences comprising a pro-peptide position −1 refers to the amino acid of the signal peptide sequence which is immediately adjacent the N-terminus of the first amino acid of the pro-peptide, examples of such signal peptide sequences are disclosed in WO2004/009819 (incorporated herein by reference); 
     an albumin signal peptide which is modified to comprise the pentapeptide motif of SEQ ID NO: 20, the pentapeptide motif may be located in the hydrophobic domain of the signal peptide sequence, an example of such a modified signal peptide sequence is provided in SEQ ID NO: 21. The pentapeptide motif may be inserted into an invertase signal peptide to generate a modified invertase signal peptide, examples of modified invertase signal peptides are provided in SEQ ID NO: 41 and SEQ ID NO: 42; or an albumin signal peptide which is modified to comprise the pentapeptide motif of SEQ ID NO: 20 and comprises a pro-peptide at the C′ terminus of the signal peptide sequence, the pentapeptide motif may be located in the hydrophobic domain of the signal peptide sequence, examples of such a modified signal peptide sequence are provided in SEQ ID NO: 22, SEQ ID NO: 23 and SEQ ID NO: 24. 
     Signal peptides comprising of or consisting of SEQ ID NO: 19, SEQ ID NO: 24 and SEQ ID NO: 42 are especially preferred, for example for expression of albumin or a variant, fragment and/or fusion thereof. 
     Other useful signal peptide coding sequences are described by Romanos et al., 1992, supra. 
     The control sequence may also be a pro-peptide coding sequence that encodes a pro-peptide positioned at the N-terminus of a polypeptide. The resultant polypeptide is known as a proenzyme or pro-polypeptide (or a zymogen in some cases). A pro-polypeptide is generally inactive and can be converted to an active polypeptide by catalytic or autocatalytic cleavage of the pro-peptide from the pro-polypeptide. The pro-peptide coding sequence may be obtained from the genes for  Saccharomyces cerevisiae  alpha-factor. 
     Where both signal peptide and pro-peptide sequences are present, the pro-peptide sequence is positioned next to the N-terminus of the polypeptide and the signal peptide sequence is positioned next to the N-terminus of the pro-peptide sequence. 
     It may also be desirable to add regulatory sequences that regulate expression of the polypeptide relative to the growth of the host cell. Examples of regulatory systems are those that cause expression of the gene to be turned on or off in response to a chemical or physical stimulus, including the presence of a regulatory compound. In yeast, the ADH2 system or GAL1 system may be used. In filamentous fungi, the  Aspergillus nigerglucoamylase  promoter,  Aspergillus oryzae  TAKA alpha-amylase promoter, and  Aspergillus oryzae  glucoamylase promoter may be used. Other examples of regulatory sequences are those that allow for gene amplification. In eukaryotic systems, these regulatory sequences include the dihydrofolate reductase gene that is amplified in the presence of methotrexate, and the metallothionein genes that are amplified with heavy metals. In these cases, the polynucleotide encoding the polypeptide would be operably linked with the regulatory sequence. 
     The host strain may or may not express or overexpress one or more chaperone proteins such as those described in WO2005/061718, WO2006/067511, WO2006/136831 or WO2014/138371, all incorporated herein by reference. For example, the host strain may or may not overexpress one or more of: AHA1, CCT2, CCT3, CCT4, CCT5, CCT6, CCT7, CCT8, CNS1, CPR3, CPRE, ERO1, EUG1, FM01, HCH1, HSP10, HSP12, HSP104, HSP26, HSP30, HSP42, HSP60, HSP78, HSP82, JEM1, MDJ1, MDJ2, MPD1, MPD2, PDI1, PFD1, ABC1, APJ1, ATP11, ATP12, BTT1, CDC37, CPR7, HSC82, KAR2, LHS1, MGE1, MRS11, NOB1, ECM10, SSA1, SSA2, SSA3, SSA4, SSC1, SSE2, SIL1, SLS1, ORM1, ORM2, PERI, PTC2, PSE1, UBI4 and HAC1 or a truncated intronless HAC1 (Valkonen et al., 2003 , Applied Environ. Micro.,  69: 2065), as well as TIM9, PAM18 (also known as TIM14) and TCP1 (also known as CCT1) or a variant thereof. Overexpression of PDI1 (SEQ ID NO: 25) or variant or fragment thereof and/or ERO1 (SEQ ID NO: 26) or variant or fragment thereof is preferred. Over-expression includes increasing the expression of the chaperone by at least 25, 50, 75, 100, 200, 300, 400, 500% relative to the native level expression of the chaperone in the host cell. Over-expression may correspond to an increase in chaperone amount, or an increase in chaperone activity. Overexpression may be achieved by increasing the copy number of the gene encoding the chaperone, for example by providing a host cell comprising 2, 3, 4, 5, 6, 7, 8, 9, 10 or more copies of the gene. Preferably the variant chaperone has at least 70, 75, 80, 85, 90, 91, 92, 93, 94, 95, 96, 97, 98 or 99% sequence identity to the chaperone. Preferably the variant maintains the functional activity of the chaperone. 
     The host cell may or may not comprise at least one heterologous nucleic acid encoding a protease or a fragment and/or variant thereof. The host cell may or may not comprise at least one nucleic acid encoding a protease such as a calcium dependent serine protease such as killer expression protease (Kex2p) or a fragment and/or variant thereof. Preferably the protease variant or fragment is functional, for example have the ability to cleave polypeptides at the carboxyl end of the recognition sequence Arg-Arg/X or Lys-Arg/X. A KEX2 nucleotide sequence may comprise or consist of SEQ ID NO: 27, a Kex2p protein may comprise or consist of SEQ ID NO: 28. Variants of KEX2 and Kex2p may have at least 70, 75, 80, 85, 90, 95, 96, 97, 98, or 99% identity to SEQ ID NO: 27 and SEQ ID NO: 28, respectively. KEX2 may or may not be overexpressed. 
     A preferred host cell, most preferably  S. cerevisiae , overexpresses PDI1 and/or ERO1 and comprises at least one nucleic acid encoding Kex2p. 
     The nucleotide sequences encoding the Gsh1 protein, Not4 protein, or homolog thereof, and desired proteins can be prepared using any mutagenesis procedure known in the art, such as site-directed mutagenesis, synthetic gene construction, semi-synthetic gene construction, random mutagenesis, shuffling, etc. 
     Site-directed mutagenesis is a technique in which one or more (e.g., several) mutations are introduced at one or more defined sites in a polynucleotide encoding the parent. 
     Site-directed mutagenesis can be accomplished in vitro by PCR involving the use of oligonucleotide primers containing the desired mutation. Site-directed mutagenesis can also be performed in vitro by cassette mutagenesis involving the cleavage by a restriction enzyme at a site in the plasmid comprising a polynucleotide encoding the parent and subsequent ligation of an oligonucleotide containing the mutation in the polynucleotide. Usually the restriction enzyme that digests the plasmid and the oligonucleotide is the same, permitting sticky ends of the plasmid and the insert to ligate to one another. See, e.g., Scherer and Davis, 1979 , Proc. Natl. Acad. Sci. USA  76: 4949-4955; and Barton et al., 1990 , Nucleic Acids Res.  18: 7349-4966. 
     Site-directed mutagenesis can also be accomplished in vivo by methods known in the art. See, e.g., U.S. Patent Application Publication No. 2004/0171154; Storici et al., 2001 , Nature Biotechnol.  19: 773-776; Kren et al., 1998 , Nat. Med.  4: 285-290; and Calissano and Macino, 1996 , Fungal Genet. Newslett.  43: 15-16. 
     Any site-directed mutagenesis procedure can be used in the present invention. There are many commercial kits available that can be used to prepare polypeptides. 
     Synthetic gene construction entails in vitro synthesis of a designed polynucleotide molecule to encode a polypeptide of interest. Gene synthesis can be performed utilizing a number of techniques, such as the multiplex microchip-based technology described by Tian et al. (2004, Nature 432: 1050-1054) and similar technologies wherein oligonucleotides are synthesized and assembled upon photo-programmable microfluidic chips. 
     Single or multiple amino acid substitutions, deletions, and/or insertions can be made and tested using known methods of mutagenesis, recombination, and/or shuffling, followed by a relevant screening procedure, such as those disclosed by Reidhaar-Olson and Sauer, 1988 , Science  241: 53-57; Bowie and Sauer, 1989 , Proc. Natl. Acad. Sci. USA  86: 2152-2156; WO95/17413; or WO95/22625. Other methods that can be used include error-prone PCR, phage display (e.g., Lowman et al., 1991 , Biochemistry  30: 10832-10837; U.S. Pat. No. 5,223,409; WO92/06204) and region-directed mutagenesis (Derbyshire et al., 1986 , Gene  46: 145; Ner et al., 1988 , DNA  7: 127). 
     Mutagenesis/shuffling methods can be combined with high-throughput, automated screening methods to detect activity of cloned, mutagenized polypeptides expressed by host cells (Ness et al., 1999 , Nature Biotechnology  17: 893-896). Mutagenized DNA molecules that encode active polypeptides can be recovered from the host cells and rapidly sequenced using standard methods in the art. These methods allow the rapid determination of the importance of individual amino acid residues in a polypeptide. 
     Semi-synthetic gene construction is accomplished by combining aspects of synthetic gene construction, and/or site-directed mutagenesis, and/or random mutagenesis, and/or shuffling. Semi-synthetic construction is typified by a process utilizing polynucleotide fragments that are synthesized, in combination with PCR techniques. Defined regions of genes may thus be synthesized de novo, while other regions may be amplified using site-specific mutagenic primers, while yet other regions may be subjected to error-prone PCR or non-error prone PCR amplification. Polynucleotide subsequences may then be shuffled. 
     A second aspect of the invention provides a culture of fungal host cells containing a polynucleotide sequence encoding a desired protein, such as a heterologous protein, characterised in that the fungal host cells have a modified, such as reduced, activity level of Gsh1 protein or homolog thereof and/or a modified, such as reduced, expression level of Gsh1 protein or homolog thereof. 
     The culture of fungal host cells according to the second aspect of the invention may additionally have a modified, such as reduced, activity level of Not4 protein or homolog thereof and/or a modified, such as reduced, expression level of Not4 protein or homolog thereof. The fungal host cells according to the second aspect of the invention are as described for the first aspect of the invention. 
     Alternatively, the second aspect of the invention provides a culture of fungal host cells containing a polynucleotide sequence encoding a desired protein, such as a heterologous protein, characterised in that the fungal host cells have an increased activity level of Gsh1 protein or homolog thereof and/or an increased expression level of Gsh1 protein or homolog thereof. This may be useful for the production of a desired protein that is detrimental to the viability of the host. The fungal host cells according to this alternative second aspect of the invention are as described for the first aspect of the invention. 
     The second aspect of the invention also provides a culture of fungal host cells containing a polynucleotide sequence encoding a desired protein, such as a heterologous protein, characterised in that the fungal host cells have (i) an increased activity level of Gsh1 protein or homolog thereof and/or an increased expression level of Gsh1 protein or homolog thereof and (ii) an increased activity level of Not4 protein or homolog thereof and/or an increased expression level of Not4 protein or homolog thereof. This may be useful for the production of a desired protein that is detrimental to the viability of the host. The fungal host cells according to this alternative second aspect of the invention are as described for the first aspect of the invention. 
     The method may comprise culturing in the presence of glutathione. This is particularly useful when the fungal host lacks a functional Gsh1 protein, for example due to mutation or deletion. It may also be useful when the fungal host cell contains a functional or partially functional Gsh1 protein. Glutathione may be present in the fermentation media at at least 0.05 mM, for example from about 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450 mM to about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500 mM, preferably from about 0.5 to about 50 mM, more preferably from about 1 to about 10 mM, more preferably from about 3 to about 7 mM, most preferably at about 5 mM. 
     A third aspect of the invention provides a method for producing a desired protein, such as a heterologous protein, from a fungal host cell, the method comprising providing a fungal host cell according to the first aspect of the invention or a culture according to the second aspect of the invention and culturing the fungal host cell or culture to produce the desired protein. The method may be used to modify the production yield of a desired polypeptide from a fungal host cell. In some cases, it may be desirable to increase the production yield of one or more proteins. In other cases, it may be desirable to decrease the production yield of one or more proteins, such as proteins that may be toxic to the host cell. 
     The desired protein may or may not be secreted from the host cell, a secreted protein is preferred. 
     The host cells may be cultivated in a nutrient medium suitable for production of the desired protein using methods known in the art. For example, the cell may be cultivated by shake flask cultivation, or small-scale or large-scale fermentation (including continuous, batch, fed-batch, or solid state fermentations) in laboratory or industrial fermenters performed in a suitable medium and under conditions allowing the polypeptide to be expressed and/or isolated. The cultivation may take place in a suitable nutrient medium comprising carbon and nitrogen sources and inorganic salts, using procedures known in the art. Suitable media are available from commercial suppliers or may be prepared according to published compositions (e.g., in catalogues of the American Type Culture Collection). Preferred media include MW11D as described in Example 5. If the desired protein is secreted into the nutrient medium, the desired protein may be recovered directly from the medium. If the desired protein is not secreted, it may be recovered from cell lysates. 
     The culturing may be at small or large scale, for example microtiter plate scale (e.g. from 10 to 500 microliter culture volume media), shake flask scale (e.g. from 5 to 1000 milliliter (mL) culture volume), or fermenter or equivalent systems scale (e.g. at least from 5 mL culture volume, more preferably at least 1, 2, 3, 4 or 5 liter (L), more preferably at least 10, 50, 100 L, for example at least 500, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 20000, 30000 L culture volume). 
     The culturing may be at a pH suitable for the host cell. For  S. cerevisiae , preferably the pH is from 5 to 7, for example from 5, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, or 6.9 to 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9 or 7. A preferred pH range is about 6.0 to about 6.4. 
     The culturing may be at a temperature of from about 20° C. to about 35° C., for example from about 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34° C. to about 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34 or 35° C., preferably from about 28 to about 32° C., more preferably about 30° C. 
     The culturing may or may not involve agitation, for example rotating of the culture vessel or by use of an agitator within the culture vessel. Agitation is preferred. 
     The desired protein may be detected using methods known in the art that are specific for the desired protein. These detection methods include, but are not limited to, use of specific antibodies, or high performance liquid chromatography (HPLC). 
     A preferred HPLC is gel permeation HPLC (GP-HPLC). Suitable equipment includes a LC2010 HPLC system (Shimadzu) equipped with UV detection under Shimadzu VP7.3 client server software control. Injections of 75 μL may be made onto a 7.8 mm id×300 mm length TSK G3000SWXL column (Tosoh Bioscience), with a 6.0 mm id×40 mm length TSK SW guard column (Tosoh Bioscience). Samples may be chromatographed in 25 mM sodium phosphate, 100 mM sodium sulfate, 0.05% (w/v) sodium azide, pH 7.0 at 1 mL·min −1 , with a run time of 20 minutes. Samples may be quantified by UV detection at 280 nm, by peak area, relative to a recombinant human albumin standard of known concentration (e.g. 10 mg/mL) and corrected for their relative extinction coefficients. 
     Optionally, the method comprises recovering the desired protein, for example isolating the desired protein from the host cell or host cell culture, e.g. cell media or cell lysate. 
     The desired protein may be recovered using methods known in the art. For example, the desired protein may be recovered from the nutrient medium by conventional procedures including, but not limited to, collection, centrifugation, filtration, extraction, spray-drying, evaporation, or precipitation. 
     Optionally, the method comprises purifying the desired protein. The desired protein may be purified by a variety of procedures known in the art including, but not limited to, chromatography (e.g., ion exchange, affinity, hydrophobic, chromatofocusing, and size exclusion), electrophoretic procedures (e.g., preparative isoelectric focusing), differential solubility (e.g., ammonium sulfate precipitation), SDS-PAGE, or extraction (see, e.g.,  Protein Purification , Janson and Ryden, editors, VCH Publishers, New York, 1989) to obtain substantially pure desired proteins. 
     In an alternative aspect, the desired protein is not recovered, but rather a host cell of the present invention expressing the desired protein is used as a source of the desired protein. 
     The step of purifying the desired protein (such as a desired heterologous protein) from the cultured host cell or the culture medium optionally comprises cell immobilization, cell separation and/or cell breakage, but always comprises at least one other purification step different from the step or steps of cell immobilization, separation and/or breakage. 
     Cell immobilization techniques, such as encasing the cells using calcium alginate bead, are known in the art. Similarly, cell separation techniques, such as centrifugation, filtration (e.g. cross-flow filtration), expanded bed chromatography and the like are known in the art. Likewise, methods of cell breakage, including beadmilling, sonication, enzymatic exposure and the like are known in the art. 
     The at least one other purification step may be any other step suitable for protein purification known in the art. For example purification techniques for the recovery of recombinantly expressed albumin have been disclosed in: WO2010/128142, affinity purification using an albumin specific ligand such as 2-chloro-4,6-di(2′-sulphoanilino)-S-triazine, WO92/04367, removal of matrix-derived dye; EP464590, removal of yeast-derived colorants; EP319067, alkaline precipitation and subsequent application of the albumin to a lipophilic phase; and WO96/37515, U.S. Pat. No. 5,728,553 and WO00/44772, which describe complete purification processes; all of which are incorporated herein by reference. 
     Desired proteins other than albumin may be purified from the culture medium by any technique that has been found to be useful for purifying such proteins. 
     Suitable methods include ammonium sulfate or ethanol precipitation, acid or solvent extraction, anion or cation exchange chromatography, phosphocellulose chromatography, hydrophobic interaction chromatography, affinity chromatography, hydroxylapatite chromatography, lectin chromatography, concentration, dilution, pH adjustment, diafiltration, ultrafiltration, high performance liquid chromatography (“HPLC”), reverse phase HPLC, conductivity adjustment and the like. 
     Optionally, the method may comprise purifying the isolated protein to a commercially or industrially acceptable level of purity. By commercially or industrially acceptable level of purity, we include the provision of the protein at a concentration of at least 0.01 g·L −1 , 0.02 g·L −1 , 0.03 g·L −1 , 0.04 g·L −1 , 0.05 g·L −1 , 0.06 g·L −1 , 0.07 g·L −1 , 0.08 g·L −1 , 0.09 g·L −1 , 0.1 g·L −1 , 0.2 g·L −1 , 0.3 g·L −1 , 0.4 g·L −1 , 0.5 g·L −1 , 0.6 g·L −1 , 0.7 g·L −1 , 0.8 g·L −1 , 0.9 g·L −1 , 1 g·L −1 , 2 g·L −1 , 3 g·L −1 , 4 g·L −1 , 5 g·L −1 , 6 g·L −1 , 7 g·L −1 , 8 g·L −1 , 9 g·L −1 , 10 g·L −1 , 15 g·L −1 , 20 g·L −1 , 25 g·L −1 , 30 g·L −1 , 40 g·L −1 , 50 g·L −1 , 60 g·L −1 , 70 g·L −1 , 80 g·L −1 , 90 g·L −1 , 100 g·L −1 , 150 g·L −1 , 200 g·L −1 , 250 g·L −1 , 300 g·L −1 , 350 g·L −1 , 400 g·L −1 , 500 g·L −1 , 600 g·L −1 , 700 g·L −1 , 800 g·L −1 , 900 g·L −1 , 1000 g·L −1 , or more. By commercially or industrially acceptable level of purity, we include the provision of the isolated protein in which other material (for example, one or more (e.g. several) contaminants) are present at a level of less than 50%, 40%, 30%, 20%, 10%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.01%, 0.001%, 0.0001%, 0.00001%, or 0.000001% and, most preferably at a level of 0%. 
     The protein may be provided at a concentration of at least 0.01 g·L −1 , 0.02 g·L −1 , 0.03 Oil, 0.04 g·L −1 , 0.05 Oil, 0.06 g·L −1 , 0.07 g·L −1 , 0.08 g·L −1 , 0.09 g·L −1 , 0.1 g·L −1 , 0.2 g·L −1 , 0.3 g·L −1 , 0.4 g·L −1 , 0.5 g·L −1 , 0.6 g·L −1 , 0.7 g·L −1 , 0.8 Oil, 0.9 g·L −1 , 1 g·L −1 , 2 g·L −1 , 3 g·L −1 , 4 g·L −1 , 5 g·L −1 , 6 g·L −1 , 7 g·L −1 , 8 g·L −1 , 9 g·L −1 , 10 g·L −1 , 15 g·L −1 , 20 g·L −1 , 25 g·L −1 , 30 g·L −1 , 40 g·L −1 , 50 g·L −1 , 60 g·L −1 , 70 g·L −1 , 80 g·L −1 , 90 g·L −1 , 100 g·L −1 , 150 g·L −1 , 200 g·L −1 , 250 g·L −1 , 300 g·L −1 , 350 g·L −1 , 400 g·L −1 , 500 g·L −1 , 600 g·L −1 , 700 g·L −1 , 800 g·L −1 , 900 g·L −1 , 1000 g·L −1 , or more. 
     It is preferred that the desired protein is purified to achieve a pharmaceutically acceptable level of purity. A protein has a pharmaceutically acceptable level of purity if it is essentially pyrogen free and can be administered in a pharmaceutically efficacious amount without causing medical effects not associated with the activity of the protein. 
     Optionally, the method further comprises formulating the desired protein with a therapeutically acceptable carrier or diluent thereby to produce a therapeutic product suitable for administration to a human or an animal. 
     The resulting desired protein may, or may not, be used for any of its known utilities, which, in the case of albumin, include intra venous (i.v.) administration to patients to treat severe burns, shock and blood loss, supplementing culture media, and as an excipient in formulations of other proteins. 
     Although it is possible for a therapeutically, diagnostically, industrially, domestically or nutritionally useful desired protein obtained by a process of the invention to be presented or administered alone, it is preferable to present it as a formulation (such as a pharmaceutical formulation, particularly in the case of therapeutically and/or diagnostically useful proteins), together with one or more acceptable carriers or diluents. The carrier(s) or diluent(s) must be “acceptable” in the sense of being compatible with the desired protein and, where the formulation is intended for administration to a recipient, then not deleterious to the recipient thereof. Typically, the carriers or diluents will be water or saline which will be sterile and pyrogen free. 
     Optionally the thus formulated protein will be presented in a unit dosage form, such as in the form of a tablet, capsule, injectable solution or the like. 
     Optionally, the method further comprises providing the desired protein in unit dosage form. 
     A fourth aspect of the invention provides a method for increasing the yield of a desired protein (such as a heterologous protein) comprising the method according to the third aspect of the invention. 
     The fourth aspect of the invention also provides use of a host cell according to the first aspect of the invention or a culture according to the second aspect of the invention to increase the yield of a desired protein (such as a heterologous protein). 
     Yield refers to the amount of product, for example desired protein, in solution, for example culture broth or cell lysis mixture. Yield may be expressed in relative terms, e.g. the yield from a reference host strain being 100%. When comparing host strains, it is preferred that the yield is measured under a defined set of conditions. Absolute yield may be expressed as nanograms per microliter (ng/μL) or grams per liter (g/L). Yield may alternatively be expressed as rate of specific cellular productivity (Y PXT ). 
     Preferably, the yield of the desired protein is at least 2% higher than the yield (g/L or Y PXT ) from a reference fungal host cell such as a fungal host cell having a wild-type Gsh1 protein, such as SEQ ID NO: 2, more preferably at least 3, 4, 5, 6, 7, 8, 9, 10, 12.5, 15, 17.5, 20, 22.5, 25, 27.5, 30, 35, 40, 45, or at least 50% higher. A preferred reference fungal host cell has a Gsh1 protein of SEQ ID NO: 2. 
     Preferably, the yield of the desired protein is at least 2% higher than the yield (g/L or Y PXT ) from a reference fungal host cell such as a fungal host cell having a wild-type Not4 protein, such as SEQ ID NO: 6, more preferably at least 3, 4, 5, 6, 7, 8, 9, 10, 12.5, 15, 17.5, 20, 22.5, 25, 27.5, 30, 35, 40, 45, or at least 50% higher. A preferred reference fungal host cell has a Not4 protein of SEQ ID NO: 6. 
     Preferably, the yield of the desired protein is at least 2% higher than the yield (g/L or Y PXT ) from a reference fungal host cell such as a fungal host cell having a wild-type Gsh1 protein, such as SEQ ID NO: 2, and a wild-type Not4 protein, such as SEQ ID NO: 6, more preferably at least 3, 4, 5, 6, 7, 8, 9, 10, 12.5, 15, 17.5, 20, 22.5, 25, 27.5, 30, 35, 40, 45, or at least 50% higher. A preferred reference fungal host cell has a Gsh1 protein of SEQ ID NO: 2 and a Not4 protein of SEQ ID NO: 6. 
     The desired protein may be as described for the first aspect of the invention, especially an albumin or variant, fragment and/or fusion thereof. 
     A fifth aspect of the invention provides a desired protein (such as a heterologous protein) produced by the method according to the third or fourth aspect of the invention. 
     The invention also provides a composition, such as a pharmaceutical composition, comprising the desired protein of the fifth aspect of the invention. The pharmaceutical composition may comprise one or more pharmaceutically acceptable carriers such as those approved by a regulatory authority such as the US Food and Drug Administration or European Medicines Agency. The invention further provides a method of treating a patient comprising administering an effective amount of the pharmaceutical composition to the patient. 
     A sixth aspect of the invention provides a method of preparing a fungal host cell according to the first aspect of the invention or a culture according to the second aspect of the invention. The method comprises genetically modifying a (parent) fungal host cell to modify the resultant Gsh1 protein or homolog thereof, to modify, e.g. reduce, the activity level of Gsh1 protein or homolog thereof, to modify a GSH1 gene or homolog thereof or a control sequence thereof or to modify the expression level of a GSH1 gene or homolog thereof. Optionally, the method may also comprise genetically modifying the (parent) fungal host cell to modify the resultant Not4 protein or homolog thereof, to modify, e.g. reduce, the activity level of Not4 protein or homolog thereof, to modify a NOT4 gene or homolog thereof or a control sequence thereof or to modify the expression level of a NOT4 gene or homolog thereof. Mutations, deletions and modification of activity and/or expression levels may be as described for the first, second, and third aspects of the invention. Methods for engineering host cells are known in the art. As an alternative to genetic modification of the host cell, the level of Gsh1 protein or activity may be modified by addition of an inhibitor or enhancer to the growth media. Likewise, an alternative to genetic modification of the host cell, the level of Not4 protein or activity may be modified by addition of an inhibitor or enhancer to the growth media. 
     A seventh aspect of the invention provides a Gsh1 protein, or homolog thereof, comprising at least 50% identity to SEQ ID NO: 2 and a mutation at a position corresponding to one or more positions selected from 47, 48, 49, 50, 51, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 409, 451, 452, 453, 454 and 455 of SEQ ID NO: 2, preferably a position selected from (a) 57 to 51; (b) 120 to 130; (c) 409 or (d) 451 to 455. A mutation at a position corresponding to position 125 of SEQ ID NO: 2 is particularly preferred. 
     The Gsh1 protein according to the seventh aspect of the invention may be as described in relation to the first aspect of the invention. Preferably the Gsh1 protein comprises or consists of SEQ ID NO: 4. The Gsh1 protein of the seventh aspect of the invention may or may not be an isolated protein. 
     An eighth aspect of the invention provides a polynucleotide encoding a Gsh1 variant of the present invention, such as a variant of SEQ ID NO: 2 which results in a lower level of Gsh1 protein expression, or homolog thereof, and/or a lower activity level of Gsh1 protein, or homolog thereof, than a host cell encoding a wild-type Gsh1 protein such as SEQ ID NO: 2, or homolog thereof. Such Gsh1 proteins are described in the first to sixth aspects of the invention. 
     A preferred polynucleotide encodes a Gsh1 protein with the mutation R125G (SEQ ID NO: 4), an example of such a polynucleotide sequence is provided by SEQ ID NO: 3. 
     For example, the present invention also relates to nucleic acid constructs comprising a polynucleotide encoding a Gsh1 variant of the present invention operably linked to one or more control sequences that direct the expression of the coding sequence in a suitable host cell under conditions compatible with the control sequences. Suitable control sequences are described in the first to seventh aspects of the invention. 
     The nucleic acid construct may additionally comprise a polynucleotide encoding a Not4 variant of the present invention operably linked to one or more control sequences that direct the expression of the coding sequence in a suitable host cell under conditions compatible with the control sequences. Suitable control sequences are described in the first to sixth aspects of the invention. 
     The polynucleotide(s) may be located on a vector or in the genome of the host cell. 
     Consequently, the present invention also relates to recombinant vectors comprising a polynucleotide encoding a Gsh1 variant of the present invention, a promoter, and transcriptional and translational stop signals. Optionally, the vector further comprises a polynucleotide encoding a Not4 variant of the present invention, a promoter, and transcriptional and translational stop signals. The Gsh1 may be encoded on the same polynucleotide (e.g. vector) or on a different polynucleotide (e.g. vector) to Not4. The invention also relates to vectors comprising a polynucleotide encoding Gsh1 and one or more (e.g. several) control sequences which cause the level of Gsh1 or Gsh1 activity to be modified, for example reduced. Optionally, the polynucleotides (e.g. vectors) further comprise a polynucleotide encoding Not4 and one or more (e.g. several) control sequences which cause the level of Not4 or Not4 activity to be modified, for example reduced. The various nucleotide and control sequences may be joined together to produce a recombinant vector that may include one or more convenient restriction sites to allow for insertion or substitution of the polynucleotide encoding the variant at such sites. Alternatively, the polynucleotide may be expressed by inserting the polynucleotide or a nucleic acid construct comprising the polynucleotide into an appropriate vector for expression. In creating the vector, the coding sequence is located in the vector so that the coding sequence is operably linked with the appropriate control sequences for expression. 
     The recombinant vector may be any vector (e.g., a plasmid or virus) that can be conveniently subjected to recombinant DNA procedures and can bring about expression of the polynucleotide. The choice of the vector will typically depend on the compatibility of the vector with the host cell into which the vector is to be introduced. The vector may be a linear or closed circular plasmid. 
     The vector may be an autonomously replicating vector, i.e., a vector that exists as an extrachromosomal entity, the replication of which is independent of chromosomal replication, e.g., a plasmid, an extrachromosomal element, a minichromosome, or an artificial chromosome. The vector may contain any means for assuring self-replication. Alternatively, the vector may be one that, when introduced into the host cell, is integrated into the genome and replicated together with the chromosome(s) into which it has been integrated. Furthermore, a single vector or plasmid or two or more vectors or plasmids that together contain the total DNA to be introduced into the genome of the host cell, or a transposon, may be used. 
     The vector preferably contains one or more selectable markers that permits selection of transformed, transfected, transduced, or the like cells. A selectable marker is a gene, the product of which provides for biocide or viral resistance, resistance to heavy metals, prototrophy to auxotrophs, and the like. 
     The vector preferably contains an element(s) that permits integration of the vector into the host cell&#39;s genome or autonomous replication of the vector in the cell independent of the genome. 
     For integration into the host cell genome, the vector may rely on the polynucleotide&#39;s sequence encoding the variant or any other element of the vector for integration into the genome by homologous or non-homologous recombination. Alternatively, the vector may contain additional polynucleotides for directing integration by homologous recombination into the genome of the host cell at a precise location(s) in the chromosome(s). To increase the likelihood of integration at a precise location, the integrational elements should contain a sufficient number of nucleic acids, such as 100 to 10,000 base pairs, 400 to 10,000 base pairs, and 800 to 10,000 base pairs, which have a high degree of sequence identity to the corresponding target sequence to enhance the probability of homologous recombination. The integrational elements may be any sequence that is homologous with the target sequence in the genome of the host cell. Furthermore, the integrational elements may be non-encoding or encoding polynucleotides. On the other hand, the vector may be integrated into the genome of the host cell by non-homologous recombination. 
     For autonomous replication, the vector may further comprise an origin of replication enabling the vector to replicate autonomously in the host cell in question. The origin of replication may be any plasmid replicator mediating autonomous replication that functions in a cell. The term “origin of replication” or “plasmid replicator” means a polynucleotide that enables a plasmid or vector to replicate in vivo. 
     Examples of origins of replication for use in a yeast host cell are the 2-micron origin of replication, ARS1, ARS4, the combination of ARS1 and CEN3, and the combination of ARS4 and CEN6. 
     Examples of origins of replication useful in a filamentous fungal cell are AMA1 and ANS1 (Gems et al., 1991 , Gene  98: 61-67; Cullen et al., 1987 , Nucleic Acids Res.  15: 9163-9175; WO00/24883). Isolation of the AMA1 gene and construction of plasmids or vectors comprising the gene can be accomplished according to the methods disclosed in WO00/24883. 
     More than one copy of a polynucleotide of the present invention may be inserted into a host cell to increase production of a desired protein. An increase in the copy number of the polynucleotide can be obtained by integrating at least one additional copy of the sequence into the host cell genome or by including an amplifiable selectable marker gene with the polynucleotide where cells containing amplified copies of the selectable marker gene, and thereby additional copies of the polynucleotide, can be selected for by cultivating the cells in the presence of the appropriate selectable agent. 
     The procedures used to ligate the elements described above to construct the recombinant vectors of the present invention are known to one skilled in the art (see, e.g., Sambrook et al., 1989, Molecular Cloning, A Laboratory Manual, 2d edition, Cold Spring Harbor, N.Y.). 
     PREFERRED EMBODIMENTS 
     1. A fungal host cell having a modified: 
     
         
         
           
             a. Gsh1 protein or homolog thereof, and/or 
             b. activity level or expression level of Gsh1 protein or homolog thereof, and/or 
             c. GSH1 gene or homolog thereof, and/or 
             d. level of expression of GSH1 gene or homolog thereof.
 
2. The fungal host cell of embodiment 1, wherein the modified level is a reduced level.
 
3. The fungal host cell of embodiment 1, wherein the modified level is an increased level.
 
4. The fungal host cell of any preceding embodiment, wherein the modified level is relative to the level of a reference fungal host cell, such as:
 
             a. a fungal host cell in which the Gsh1 protein or homolog thereof is a wild-type Gsh1 protein or homolog thereof, 
             b. a fungal host cell in which the Gsh1 protein comprises or consists of SEQ ID NO: 2, 
             c.  S. cerevisiae  S288C or 
             d.  S. cerevisiae  DXY1.
 
5. The fungal host of any of embodiments 1 to 4 having a modified:
 
             e. Not4 protein or homolog thereof, and/or 
             f. activity level or expression level of Not4 protein or homolog thereof, and/or 
             g. NOT4 gene or homolog thereof, and/or 
             h. level of expression of NOT4 gene or homolog thereof,
 
6. The fungal host cell of embodiment 5, wherein the modified level is a reduced level.
 
7. The fungal host cell of embodiment 5, wherein the modified level is an increased level.
 
8. The fungal host cell of embodiment 5 or 6, wherein the modified level is relative to the level of a reference fungal host cell, such as:
 
             a. a fungal host cell in which the Not4 protein or homolog thereof is a wild-type Not4 protein or homolog thereof, 
             b. a fungal host cell in which the Not4 protein comprises or consists of SEQ ID NO: 6, 
             c.  S. cerevisiae  S288C or 
             d.  S. cerevisiae  DXY1.
 
9. The fungal host cell according to any preceding embodiment, comprising a nucleotide sequence encoding a desired protein such as heterologous protein.
 
10. The fungal host cell according to embodiment 9 in which the desired protein is selected from albumin, a monoclonal antibody, an etoposide, a serum protein (such as a blood clotting factor), antistasin, a tick anticoagulant peptide, transferrin, lactoferrin, endostatin, angiostatin, collagens, immunoglobulins or immunoglobulin-based molecules or fragment of either (e.g. a Small Modular ImmunoPharmaceutical™ (“SMIP”) or dAb, Fab′ fragments, F(ab′)2, scAb, scFv or scFv fragment), a Kunitz domain protein (such as those described in WO03/066824 (incorporated herein by reference), with or without albumin fusions), interferons, interleukins, IL-10, IL-11, IL-2, interferon α (alpha) species and sub-species, interferon β (beta) species and sub-species, interferon γ (gamma) species and sub-species, leptin, CNTF, CNTF Ax15 , IL-1-receptor antagonist, erythropoietin (EPO) and EPO mimics, thrombopoietin (TPO) and TPO mimics, prosaptide, cyanovirin-N, 5-helix, T20 peptide, T1249 peptide, HIV gp41, HIV gp120, urokinase, prourokinase, tPA, hirudin, platelet derived growth factor, parathyroid hormone, proinsulin, insulin, glucagon, glucagon-like peptides such as exendin-4, GLP-1 or GLP-2, insulin-like growth factor, calcitonin, growth hormone, transforming growth factor β (beta), tumour necrosis factor, G-CSF, GM-CSF, M-CSF, FGF, coagulation factors in both pre and active forms, including but not limited to plasminogen, fibrinogen, thrombin, pre-thrombin, pro-thrombin, von Willebrand&#39;s factor, alpha 1 -antitrypsin, plasminogen activators, Factor VII, Factor VIII, Factor IX, Factor X and Factor XIII, nerve growth factor, LACI, platelet-derived endothelial cell growth factor (PD-ECGF), glucose oxidase, serum cholinesterase, aprotinin, amyloid precursor protein, inter-alpha trypsin inhibitor, antithrombin III, apo-lipoprotein species, Protein C, Protein S, a metabolite, an antibiotic, or a variant or fragment of any of the above.
 
11. The fungal host cell according to embodiment 9 or 10 in which the desired protein comprises or consists of an albumin, variant, fragment and/or fusion thereof.
 
12. The fungal host cell according to embodiment 11 in which the albumin or variant, fragment and/or fusion thereof has at least 70% identity to SEQ ID NO: 10.
 
13. The fungal host cell according to embodiment 11 in which the albumin or variant, fragment and/or fusion thereof has at least 75, 80, 85, 90, 91, 92, 93, 95, 96, 97, 98 or 99% identity to SEQ ID NO: 10.
 
14. The fungal host cell according to embodiment 13 in which the albumin or variant, fragment and/or fusion thereof has at least 70% identity to SEQ ID NO: 10, preferably at least 75, 80, 85, 90, 91, 92, 93, 95, 96, 97, 98 or 99% identity to SEQ ID NO: 10, and comprises A, C, D, E, F, G, H, I, L, M, N, P, Q, R, S, T, V, W or Y at a position corresponding to K573 of SEQ ID NO: 10.
 
15. The fungal host cell according to embodiment 14 in which albumin or variant, fragment and/or fusion thereof comprises a P, H, W or Y at a position corresponding to K573 of SEQ ID NO: 10.
 
16. The fungal host cell according to embodiment 15 in which the albumin variant, fragment and/or fusion thereof has at least 98% identity to SEQ ID NO: 10, and comprises a P at a position corresponding to K573 of SEQ ID NO: 10.
 
17. The fungal host cell according to any of embodiments 13 to 16 in which the albumin or variant, fragment and/or fusion thereof has at least 70% identity to SEQ ID NO: 10, preferably at least 75, 80, 85, 90, 91, 92, 93, 95, 96, 97, 98 or 99% identity to SEQ ID NO: 10, and comprises A, C, D, F, G, H, I, K, L, M, N, P, Q, R, S, T, V, W or Y at a position corresponding to E492 of SEQ ID NO: 10.
 
18. The fungal host cell according to embodiment 17 in which albumin or variant, fragment and/or fusion thereof comprises a G, D, F, H, M or R at a position corresponding to E492 of SEQ ID NO: 10.
 
19. The fungal host cell according to embodiment 18 in which the albumin variant, fragment and/or fusion thereof has at least 98% identity to SEQ ID NO: 10, and comprises a G or D at a position corresponding to E492 of SEQ ID NO: 10.
 
20. The fungal host cell according to embodiment 19 in which the albumin variant, fragment and/or fusion thereof has at least 98% identity to SEQ ID NO: 10, and comprises a G at a position corresponding to E492 of SEQ ID NO: 10.
 
21. The fungal host cell according to any of embodiments 13 to 20 in which the albumin or variant, fragment and/or fusion thereof has at least 70% identity to SEQ ID NO: 10, preferably at least 75, 80, 85, 90, 91, 92, 93, 95, 96, 97, 98 or 99% identity to SEQ ID NO: 10, and comprises A, C, D, E, F, G, H, I, L, M, N, P, Q, R, S, T, V, W or Y at a position corresponding to K574 of SEQ ID NO: 10.
 
22. The fungal host cell according to embodiment 21 in which albumin or variant, fragment and/or fusion thereof comprises a H, G, D, F, N, S or Y at a position corresponding to K574 of SEQ ID NO: 10.
 
23. The fungal host cell according to embodiment 22 in which the albumin variant, fragment and/or fusion thereof has at least 98% identity to SEQ ID NO: 10, and comprises a D, F, G or H at a position corresponding to K574 of SEQ ID NO: 10.
 
24. The fungal host cell according to embodiment 23 in which the albumin variant, fragment and/or fusion thereof has at least 98% identity to SEQ ID NO: 10, and comprises an H at a position corresponding to K574 of SEQ ID NO: 10.
 
25. The fungal host cell according to any of embodiments 13 to 24 in which the albumin or variant, fragment and/or fusion thereof has at least 70% identity to SEQ ID NO: 10, preferably at least 75, 80, 85, 90, 91, 92, 93, 95, 96, 97, 98 or 99% identity to SEQ ID NO: 10, and comprises A, C, D, E, F, G, H, I, K, L, M, N, P, R, S, T, V, W or Y at a position corresponding to Q580 of SEQ ID NO: 10.
 
26. The fungal host cell according to embodiment 25 in which albumin or variant, fragment and/or fusion thereof comprises a K or R at a position corresponding to Q580 of SEQ ID NO: 10.
 
27. The fungal host cell according to embodiment 26 in which the albumin variant, fragment and/or fusion thereof has at least 98% identity to SEQ ID NO: 10, and comprises a K at a position corresponding to K573 of SEQ ID NO: 10.
 
28. The fungal host cell according to any of embodiments 13 to 26 in which the albumin fusion comprises the albumin variant of SEQ ID NO: 45.
 
29. The fungal host cell according to any of embodiments 13 to 26 in which the albumin variant comprises or consists of SEQ ID NO: 45.
 
30. The fungal host cell according to any of embodiments 11 to 29 in which the fusion comprises a fusion partner which is not albumin or a variant or a fragment or fusion thereof.
 
31. The fungal host cell according to any of embodiments 12 to 30 in which the fusion comprises a fusion partner selected from monoclonal antibody, an etoposide, a serum protein (such as a blood clotting factor), antistasin, a tick anticoagulant peptide, transferrin, lactoferrin, endostatin, angiostatin, collagens, immunoglobulins or immunoglobulin-based molecules or fragment of either (e.g. a Small Modular ImmunoPharmaceutical™ (“SMIP”) or dAb, Fab′ fragments, F(ab′)2, scAb, scFv or scFv fragment), a Kunitz domain protein (such as those described in WO03/066824 (incorporated herein by reference), interferons, interleukins, IL-10, IL-11, IL-2, interferon α (alpha) species and sub-species, interferon β (beta) species and sub-species, interferon γ (gamma) species and sub-species, leptin, CNTF, CNTF Ax15 , IL-1-receptor antagonist, erythropoietin (EPO) and EPO mimics, thrombopoietin (TPO) and TPO mimics, prosaptide, cyanovirin-N, 5-helix, T20 peptide, T1249 peptide, HIV gp41, HIV gp120, urokinase, prourokinase, tPA, hirudin, platelet derived growth factor, parathyroid hormone, proinsulin, insulin, glucagon, glucagon-like peptides such as exendin-4, GLP-1 or GLP-2, insulin-like growth factor, calcitonin, growth hormone, transforming growth factor β (beta), tumour necrosis factor, G-CSF, GM-CSF, M-CSF, FGF, coagulation factors in both pre and active forms, including but not limited to plasminogen, fibrinogen, thrombin, pre-thrombin, pro-thrombin, von Willebrand&#39;s factor, alpha 1 -antitrypsin, plasminogen activators, Factor VII, Factor VIII, Factor IX, Factor X and Factor XIII, nerve growth factor, LACI, platelet-derived endothelial cell growth factor (PD-ECGF), glucose oxidase, serum cholinesterase, aprotinin, amyloid precursor protein, inter-alpha trypsin inhibitor, antithrombin III, apo-lipoprotein species, Protein C, Protein S, a metabolite, an antibiotic, or a variant or fragment of any of the above.
 
32. The fungal host cell according to embodiment 30 or 31 in which the fusion partner comprises or consists of a glucagon-like protein or analog thereof.
 
33. The fungal host cell according to embodiment 32 in which the fusion partner comprises or consists of SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 51, or SEQ ID NO: 52.
 
34. The fungal host cell according any of embodiments 9 to 33 in which the desired protein comprises or consists of SEQ ID NO: 16.
 
35. The fungal host cell according to any preceding embodiment in which the modified activity level and/or expression level of Gsh1 protein or homolog thereof is relative to the activity level or expression level of Gsh1 protein or homolog thereof of a parent fungal host cell such as a wild-type fungal host cell.
 
36. The fungal host cell according to embodiment 35, in which the activity level and/or expression level of Gsh1 protein or homolog thereof is reduced to no more than 99% of the activity level or expression level of Gsh1 protein or homolog thereof of the parent fungal host cell.
 
37. The fungal host cell according to embodiment 36, in which the activity level and/or expression level of Gsh1 protein or homolog thereof is reduced to no more than 95% of the activity level or expression level of Gsh1 protein or homolog thereof of the parent fungal host cell.
 
38. The fungal host cell according to embodiment 37, in which the activity level and/or expression level of Gsh1 protein or homolog thereof is reduced to no more than 90% of the activity level or expression level of Gsh1 protein or homolog thereof of the parent fungal host cell.
 
39. The fungal host cell according to embodiment 38, in which the activity level and/or expression level of Gsh1 protein or homolog thereof is reduced to no more than 80% of the activity level or expression level of Gsh1 protein or homolog thereof of the parent fungal host cell.
 
40. The fungal host cell according to embodiment 39, in which the activity level and/or expression level of Gsh1 protein or homolog thereof is reduced to no more than 70% of the activity level or expression level of Gsh1 protein or homolog thereof of the parent fungal host cell.
 
41. The fungal host cell according to embodiment 40, in which the activity level and/or expression level of Gsh1 protein or homolog thereof is reduced to no more than 60% of the activity level or expression level of Gsh1 protein or homolog thereof of the parent fungal host cell.
 
42. The fungal host cell according to embodiment 41 in which the activity level and/or expression level of Gsh1 protein or homolog thereof is reduced to no more than 50% of the activity level or expression level of Gsh1 protein or homolog thereof of the parent fungal host cell.
 
43. The fungal host cell according to embodiment 42, in which the activity level and/or expression level of Gsh1 protein or homolog thereof is reduced to no more than 40% of the activity level or expression level of Gsh1 protein or homolog thereof of the parent fungal host cell.
 
44. The fungal host cell according to embodiment 43, in which the activity level and/or expression level of Gsh1 protein or homolog thereof is reduced to no more than 30%, preferably not more than 20%, of the activity level or expression level of Gsh1 protein or homolog thereof of the parent fungal host cell.
 
45. The fungal host cell according to embodiment 44, in which the activity level and/or expression level of Gsh1 protein or homolog thereof is reduced to substantially 0% of the activity level or expression level of Gsh1 protein or homolog thereof of the parent fungal host cell.
 
46. The fungal host cell according to any preceding embodiment, in which the host cell lacks a functional GSH1 gene or homolog thereof or functional Gsh1 protein or homolog thereof.
 
47. The fungal host cell according to any preceding embodiment, in which the host cell lacks a GSH1 gene or homolog thereof or Gsh1 protein or homolog thereof.
 
48. The fungal host cell according to any preceding embodiment in which the Gsh1 protein or homolog thereof comprises a mutation at position corresponding to a position selected from 47, 48, 49, 50, 51, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 409, 451, 452, 453, 454 and 455 of SEQ ID NO: 2.
 
49. The fungal host cell according to embodiment 48 in which the position corresponds to R125 of SEQ ID NO: 2.
 
50. The fungal host cell according to embodiment 48 or 49 in which the position corresponds to H409 of SEQ ID NO: 2.
 
51. The fungal host cell according to any of embodiments 48 to 50 in which the position corresponds to P453 of SEQ ID NO: 2.
 
52. The fungal host cell according to any of embodiments 48 to 51 in which the mutation is a substitution, preferably to a non-conserved amino acid.
 
53. The fungal host cell according to embodiment 52 in which the mutation at a position corresponding to position 125 of SEQ ID NO: 2 is a substitution to A, C, D, E, F, G, H, I, L, M, N, P, Q, S, T, V, W or Y, preferably to C, D, E or G, more preferably to G.
 
54. The fungal host cell according to any of embodiments 48 to 53 in which the mutation at a position corresponding to position 125 of SEQ ID NO: 2 is from a positively charged amino acid to an aliphatic, aromatic, hydrophobic, small, tiny, polar or negatively charged amino acid, preferably a negatively charged amino acid to a tiny amino acid.
 
55. The fungal host cell according to any of embodiments 48 to 54 in which the mutation at a position corresponding to position D49 of SEQ ID NO: 2 is a substitution to A, C, F, G, H, I, K, L, M, N, P, Q, R, S, T, V, W or Y, preferably to H, K or R, more preferably to K or R.
 
56. The fungal host cell according to any of embodiment 48 to 55 in which the mutation at a position corresponding to position 49 of SEQ ID NO: 2 is from a negatively charged amino acid to a positively charged amino acid.
 
57. The fungal host cell according to any of embodiments 48 to 56 in which the mutation at a position corresponding to position H409 of SEQ ID NO: 2 is a substitution to A, C, D, E, F, G, I, K, L, M, N, P, Q, R, S, T, V, W or Y, preferably to A, I, L, V, M, F, W, Y, more preferably to A, I, L, V, most preferably to L.
 
58. The fungal host cell according to any of embodiments 48 to 57 in which the mutation at a position corresponding to position H409 of SEQ ID NO: 2 is from an aromatic amino acid to an aliphatic amino acid.
 
59. The fungal host cell according to any of embodiments 48 to 58 in which the mutation at a position corresponding to position P453 of SEQ ID NO: 2 is a substitution to A, C, D, E, F, G, H, I, K, L, M, N, Q, R, S, T, V, W or Y, preferably to A, I, L, V, M, F, W, Y, more preferably to A, I, L, V, most preferably to L.
 
60. The fungal host cell according any of embodiments 48 to 59 in which the mutation at a position corresponding to position P453 of SEQ ID NO: 2 is from an aromatic amino acid to an aliphatic amino acid.
 
61. The fungal host cell according to any preceding embodiment in which the Gsh1 protein comprises or consists of SEQ ID NO: 4.
 
62. The fungal host cell according to any preceding embodiment comprising a modified GSH1 gene, for example a polynucleotide encoding SEQ ID NO: 4.
 
63. The fungal host cell according to any of embodiments 5 to 62 in which the modified activity level or expression level of Not4 protein or homolog thereof is relative to the activity level or expression level of Not4 protein or homolog thereof of a parent fungal host cell such as a wild-type fungal host cell.
 
64. The fungal host cell according to embodiment 63, in which the activity level and/or expression level of Not4 protein or homolog thereof is reduced to no more than 90% of the activity level and/or expression level of Not4 protein or homolog thereof of the parent fungal host cell.
 
65. The fungal host cell according to embodiment 64, in which the activity level and/or expression level of Not4 protein or homolog thereof is reduced to no more than 80% of the activity level and/or expression level of Not4 protein or homolog thereof of the parent fungal host cell.
 
66. The fungal host cell according to embodiment 65, in which the activity level and/or expression level of Not4 protein or homolog thereof is reduced to no more than 70% of the activity level and/or expression level of Not4 protein or homolog thereof of the parent fungal host cell.
 
67. The fungal host cell according to embodiment 66, in which the activity level and/or expression level of Not4 protein or homolog thereof is reduced to no more than 60% of the activity level and/or expression level of Not4 protein or homolog thereof of the parent fungal host cell.
 
68. The fungal host cell according to embodiment 67, in which the activity level and/or expression level of Not4 protein or homolog thereof is reduced to no more than 50% of the activity level and/or expression level of Not4 protein or homolog thereof of the parent fungal host cell.
 
69. The fungal host cell according to embodiment 68, in which the activity level and/or expression level of Not4 protein or homolog thereof is reduced to no more than 40% of the activity level and/or expression level of Not4 protein or homolog thereof of the parent fungal host cell.
 
70. The fungal host cell according to embodiment 69, in which the activity level and/or expression level of Not4 protein or homolog thereof is reduced to no more than 30% of the activity level and/or expression level of Not4 protein or homolog thereof of the parent fungal host cell.
 
71. The fungal host cell according to embodiment 70, in which the activity level and/or expression level of Not4 protein or homolog thereof is reduced to no more than 20% of the activity level and/or expression level of Not4 protein or homolog thereof of the parent fungal host cell.
 
72. The fungal host cell according to embodiment 71, in which the activity level and/or expression level of Not4 protein or homolog thereof is reduced to substantially 0% of the activity level and/or expression level of Not4 protein or homolog thereof of the parent fungal host cell.
 
73. The fungal host cell according to any of embodiments 5 to 72, in which the host cell lacks a functional NOT4 gene or homolog thereof or functional Not4 protein or homolog thereof.
 
74. The fungal host cell according to any of embodiments 5 to 73, in which the host cell lacks a NOT4 gene or homolog thereof or Not4 protein or homolog thereof.
 
75. The fungal host cell according to any of embodiments 5 to 74, in which the NOT4 gene or homolog thereof or Not4 protein or homolog thereof is mutated to alter the interaction of the Not4 protein or homolog thereof with a Nott protein or homolog thereof.
 
76. The fungal host cell according to any of embodiments 5 to 75 in which the Not4 protein or homolog thereof comprises a mutation at position corresponding to a position selected from 426, 427, 428, 429, 430, 431, 432, 433, 434, 435, 436, 437, 438, 439, 440, 441, 442, 443, 444, 445, 446, 447, 448, 449, 450, 451, 452, 453, 454, 455, 456, 457, 458, 459, 460, 461, 462, 463, 464, 465, 466, 467, 468, 469 or 470 of SEQ ID NO: 6.
 
77. The fungal host cell according to embodiment 76 in which the position is selected from a position corresponding to 429, 430, 434, or 437 of SEQ ID NO: 6.
 
78. The fungal host cell according to embodiment 76 or 77 in which the position is selected from a position corresponding to 463, 464 or 466 of SEQ ID NO: 6.
 
79. The fungal host cell according to any of embodiments 76 to 78 in which the position is selected from a position corresponding to 442, 445, 447 or 452 of SEQ ID NO: 6.
 
80. The fungal host cell according to any of embodiments 76 to 79 in which the mutation is a substitution, preferably to a non-conserved amino acid.
 
81. The fungal host cell according to any of embodiments 76 to 80 in which the mutation at a position corresponding to position 429 of SEQ ID NO: 6 is a substitution to A, C, D, E, G, H, I, K, L, M, N, P, Q, R, S, T, V, W or Y, preferably to G, A, V, L or I, more preferably to I, L or V, most preferably to I.
 
82. The fungal host cell according to any of embodiments 76 to 81, in which the mutation at a position corresponding to position 429 of SEQ ID NO: 6 is a substitution from an aromatic amino acid to an aliphatic amino acid.
 
83. The fungal host cell according to any of embodiments 76 to 82 in which the Not4 protein comprises or consists of SEQ ID NO: 8.
 
84. The fungal host cell according to any preceding embodiment comprising a modified NOT4 gene, for example a polynucleotide encoding SEQ ID NO: 8.
 
85. The fungal host cell according to any preceding embodiment in which the host cell lacks a NOT4 gene or homolog thereof or Not4 protein or homolog thereof.
 
86. The fungal host cell according to any preceding embodiment, in which one or more of the following chaperones is overexpressed: AHA1, CCT2, CCT3, CCT4, CCT5, CCT6, CCT7, CCT8, CNS1, CPR3, CPRE, ERO1, EUG1, FM01, HCH1, HSP10, HSP12, HSP104, HSP26, HSP30, HSP42, HSP60, HSP78, HSP82, JEM1, MDJ1, MDJ2, MPD1, MPD2, PDI1, PFD1, ABC1, APJ1, ATP11, ATP12, BTT1, CDC37, CPR7, HSC82, KAR2, LHS1, MGE1, MRS11, NOB1, ECM10, SSA1, SSA2, SSA3, SSA4, SSC1, SSE2, SIL1, SLS1, ORM1, ORM2, PERI, PTC2, PSE1, UBI4 and HAC1 or a truncated intronless HAC1, TIM9, PAM18, TCP1 or a variant thereof.
 
87. The fungal host cell according to any preceding embodiment in which KEX2, or a variant or fragment thereof, is expressed or overexpressed.
 
88. The fungal host cell according to embodiment 86 or 87 in which PDI1 or a variant thereof is overexpressed or ERO1 or a variant thereof is overexpressed.
 
89. The fungal host cell according to embodiment 86 or 87 in which PDI1 or a variant thereof is overexpressed and ERO1 or a variant thereof are overexpressed.
 
90. The fungal host cell according to embodiment 86 or 87 in which PDI1 or a variant thereof is overexpressed and KEX2 or a variant thereof is expressed or overexpressed.
 
91. The fungal host cell according to embodiment 86 or 87 in which ERO1 or a variant thereof is overexpressed and KEX2 or a variant thereof is expressed or overexpressed.
 
92. The fungal host cell according to any of embodiments 86 to 91 in which PDI1 or a variant thereof is overexpressed and ERO1 or a variant thereof is overexpressed and KEX2 or a variant thereof is expressed or overexpressed.
 
93. The fungal host cell according to any preceding embodiment in which the fungal host is a yeast or a filamentous fungus.
 
94. The fungal host cell, according to any preceding embodiment, in which the host cell is a  Saccharomyces, Candida, Hansenula, Kluyveromyces, Pichia, Saccharomyces, Schizosaccharomyces , or  Yarrowia.  
 
95. The fungal host cell according to embodiment 94 in which the  Saccharomyces  is a  Saccharomyces carlsbergensis, Saccharomyces cerevisiae, Saccharomyces diastaticus, Saccharomyces douglasii, Saccharomyces kluyveri, Saccharomyces norbensis , or  Saccharomyces oviformis , preferably  Saccharomyces cerevisiae.  
 
96. A culture of fungal host cells containing a polynucleotide sequence encoding a desired protein, such as a heterologous protein, characterised in that the fungal host cells have a reduced activity level and/or expression level of Gsh1 protein or homolog thereof.
 
97. The culture of fungal host cells according to embodiment 96, having a reduced activity level and/or expression level of Not4 protein or homolog thereof.
 
98. The culture of fungal host cells of embodiment 96 or 97 in which the host cells are as defined in any of embodiments 1 to 95.
 
99. A method for producing a desired protein, such as a heterologous protein, from a fungal host cell comprising:
 
             a. providing a fungal host cell according to any of embodiments 1 to 94 or a culture according to any of embodiments 96 to 98, 
             b. culturing the fungal host cell or culture to produce the desired protein, 
             c. optionally recovering the desired protein, 
             d. optionally purifying the desired protein, 
             e. optionally formulating the desired protein with a therapeutically acceptable carrier or diluent thereby to produce a therapeutic product suitable for administration to a human or an animal, and 
             f. optionally providing the desired protein in unit dosage form.
 
100. A method for increasing the yield of a desired protein (such as a heterologous protein) comprising:
 
             a. providing a fungal host cell (such as a yeast or a filamentous fungus) having a modified:
           1. Gsh1 protein or homolog thereof, and/or   2. level of activity (preferably reduced) of Gsh1 protein or homolog thereof, and/or   3. GSH1 gene or homolog thereof, and/or   4. level of expression (preferably reduced) of GSH1 gene or homolog thereof,   such as a fungal host cell according to any of embodiments 1 to 94, and   
         
             b. culturing the host cell to produce the desired protein, and 
             c. optionally recovering the desired protein, 
             d. optionally purifying the desired protein, 
             e. optionally formulating the desired protein with a therapeutically acceptable carrier or diluent thereby to produce a therapeutic product suitable for administration to a human or an animal, and 
             f. optionally providing the desired protein in unit dosage form.
 
101. The method according to embodiment 99 or 100 in which the culturing is in the presence of glutathione.
 
102. The method according to embodiment 101 in which the glutathione is present at at least 0.05 mM.
 
103. The method according to embodiment 102 in which the glutathione is present at from about 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450 mM to about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500 mM.
 
104. The method according to embodiment 103 in which the glutathione is present at from about 1 to about 10 mM.
 
105. The method according to embodiment 104 in which the glutathione is present at from about 3 to about 7 mM.
 
106. The method according to embodiment 105 in which the glutathione is present at about 5 mM.
 
107. The method according to any of embodiments 99 to 106 in which the yield of the desired protein is at least 2% higher than the yield from a reference fungal host cell such as a fungal host cell having a wild-type Gsh1 protein, such as SEQ ID NO: 2.
 
108. The method according to embodiment 107 in which the yield is at least 3, 4, 5, 6, 7, 8, 9, 10, 12.5, 15, 17.5, 20, 22.5, 25, 27.5, 30, 35, 40, 45, or at least 50% higher than the yield from a reference fungal host cell.
 
109. The method according to embodiment 107 or 108 in which the yield of the desired protein is at least 2% higher than the yield from a reference fungal host cell such as a fungal host cell having a Gsh1 protein of SEQ ID NO: 2.
 
110. The method according to embodiment 109 in which the yield is at least 3, 4, 5, 6, 7, 8, 9, 10, 12.5, 15, 17.5, 20, 22.5, 25, 27.5, 30, 35, 40, 45, or at least 50% higher than the yield from a reference fungal host cell.
 
111. The method according to any of embodiments 99 to 110, in which the fungal host cell has a modified:
 
             1. Not4 protein or homolog thereof, and/or 
             2. level of activity (preferably reduced) of Not4 protein or homolog thereof, and/or 
             3. NOT4 gene or homolog thereof, and/or 
             4. level of expression (preferably reduced) of NOT4 gene or homolog thereof such as a fungal host cell according to any of embodiments 5 to 95.
 
112. The method according to embodiment 111 in which the yield of the desired protein is at least 2% higher than the yield from a reference fungal host cell such as a fungal host cell having a wild-type Not4 protein, such as SEQ ID NO: 6.
 
113. The method according to embodiment 112 in which the yield is at least 3, 4, 5, 6, 7, 8, 9, 10, 12.5, 15, 17.5, 20, 22.5, 25, 27.5, 30, 35, 40, 45, or at least 50% higher than the yield from a reference fungal host cell such as a fungal host cell having a wild-type Not4 protein, such as SEQ ID NO: 6.
 
114. The method according to any of embodiments 111 to 113 in which the yield of the desired protein is at least 2% higher than the yield from a reference fungal host cell such as a fungal host cell having a Gsh1 protein of SEQ ID NO: 2.
 
115. The method according to embodiment 114 in which the yield is at least 3, 4, 5, 6, 7, 8, 9, 10, 12.5, 15, 17.5, 20, 22.5, 25, 27.5, 30, 35, 40, 45, or at least 50% higher than the yield from a reference fungal host cell such as a fungal host cell having Gsh1 protein of SEQ ID NO: 2.
 
116. The method according to any of embodiments 111 to 115 in which the yield of the desired protein is at least 2% higher than the yield from a reference fungal host cell such as a fungal host cell having Gsh1 protein of SEQ ID NO: 2 and Not4 protein of SEQ ID NO: 6.
 
117. The method according to embodiment 116 in which the yield of the desired protein is at least 3, 4, 5, 6, 7, 8, 9, 10, 12.5, 15, 17.5, 20, 22.5, 25, 27.5, 30, 35, 40, 45, or at least 50% higher than the yield from a reference fungal host cell such as a fungal host cell having Gsh1 protein of SEQ ID NO: 2 and Not4 protein of SEQ ID NO: 6.
 
118. The method according to any of embodiments 99 to 117 in which the desired protein is selected from albumin, a monoclonal antibody, an etoposide, a serum protein (such as a blood clotting factor), antistasin, a tick anticoagulant peptide, transferrin, lactoferrin, endostatin, angiostatin, collagens, immunoglobulins or immunoglobulin-based molecules or fragment of either (e.g. a Small Modular ImmunoPharmaceutical™ (“SMIP”) or dAb, Fab′ fragments, F(ab′)2, scAb, scFv or scFv fragment), a Kunitz domain protein (such as those described in WO03/066824 (incorporated herein by reference), with or without albumin fusions), interferons, interleukins, IL-10, IL-11, IL-2, interferon α (alpha) species and sub-species, interferon β (beta) species and sub-species, interferon γ (gamma) species and sub-species, leptin, CNTF, CNTF Ax15 , IL-1-receptor antagonist, erythropoietin (EPO) and EPO mimics, thrombopoietin (TPO) and TPO mimics, prosaptide, cyanovirin-N, 5-helix, T20 peptide, T1249 peptide, HIV gp41, HIV gp120, urokinase, prourokinase, tPA, hirudin, platelet derived growth factor, parathyroid hormone, proinsulin, insulin, glucagon, glucagon-like peptides such as exendin-4, GLP-1 or GLP-2, insulin-like growth factor, calcitonin, growth hormone, transforming growth factor β (beta), tumour necrosis factor, G-CSF, GM-CSF, M-CSF, FGF, coagulation factors in both pre and active forms, including but not limited to plasminogen, fibrinogen, thrombin, pre-thrombin, pro-thrombin, von Willebrand&#39;s factor, alpha 1 -antitrypsin, plasminogen activators, Factor VII, Factor VIII, Factor IX, Factor X and Factor XIII, nerve growth factor, LACI, platelet-derived endothelial cell growth factor (PD-ECGF), glucose oxidase, serum cholinesterase, aprotinin, amyloid precursor protein, inter-alpha trypsin inhibitor, antithrombin III, apo-lipoprotein species, Protein C, Protein S, a metabolite, an antibiotic, or a variant or fragment of any of the above.
 
119. The method according to any of embodiments 99 to 118 in which the desired protein comprises or consists of an albumin or variant, fragment and/or fusion thereof.
 
120. The method according to embodiment 119 in which the albumin or variant, fragment and/or fusion thereof has at least 70% identity to SEQ ID NO: 10.
 
121. The method according to embodiment 120 in which the albumin or variant, fragment and/or fusion thereof has at least 75, 80, 85, 90, 91, 92, 93, 95, 96, 97, 98 or 99% identity to SEQ ID NO: 10.
 
122. The method according to embodiment 121 in which the albumin or variant, fragment and/or fusion thereof has at least 70% identity to SEQ ID NO: 10, preferably at least 75, 80, 85, 90, 91, 92, 93, 95, 96, 97, 98 or 99% identity to SEQ ID NO: 10, and comprises an A, C, D, E, F, G, H, I, L, M, N, P, Q, R, S, T, V, W or Y at a position corresponding to K573 of SEQ ID NO: 10.
 
123. The method according to embodiment 122 in which the albumin or variant, fragment and/or fusion thereof comprises a P, H, W or Y at a position corresponding to K573 of SEQ ID NO: 10.
 
124. The method according to embodiment 123 in which the albumin or variant, fragment and/or fusion thereof has at least 98% identity to SEQ ID NO: 10, and comprises a P at a position corresponding to K573 of SEQ ID NO: 10.
 
125. The method according to any of embodiments 119 to 124 in which the fusion comprises a fusion partner which is a not albumin or a variant, fragment and/or fusion thereof.
 
126. The method according to any of embodiments 120 to 125 in which the fusion comprises a fusion partner selected from monoclonal antibody, an etoposide, a serum protein (such as a blood clotting factor), antistasin, a tick anticoagulant peptide, transferrin, lactoferrin, endostatin, angiostatin, collagens, immunoglobulins or immunoglobulin-based molecules or fragment of either (e.g. a Small Modular ImmunoPharmaceutical™ (“SMIP”) or dAb, Fab′ fragments, F(ab′)2, scAb, scFv or scFv fragment), a Kunitz domain protein (such as those described in WO03/066824 (incorporated herein by reference), interferons, interleukins, IL-10, IL-11, IL-2, interferon α (alpha) species and sub-species, interferon β (beta) species and sub-species, interferon γ (gamma) species and sub-species, leptin, CNTF, CNTF Ax15 , IL-1-receptor antagonist, erythropoietin (EPO) and EPO mimics, thrombopoietin (TPO) and TPO mimics, prosaptide, cyanovirin-N, 5-helix, T20 peptide, T1249 peptide, HIV gp41, HIV gp120, urokinase, prourokinase, tPA, hirudin, platelet derived growth factor, parathyroid hormone, proinsulin, insulin, glucagon, glucagon-like peptides such as exendin-4, GLP-1 or GLP-2, insulin-like growth factor, calcitonin, growth hormone, transforming growth factor β (beta), tumour necrosis factor, G-CSF, GM-CSF, M-CSF, FGF, coagulation factors in both pre and active forms, including but not limited to plasminogen, fibrinogen, thrombin, pre-thrombin, pro-thrombin, von Willebrand&#39;s factor, alpha 1 -antitrypsin, plasminogen activators, Factor VII, Factor VIII, Factor IX, Factor X and Factor XIII, nerve growth factor, LACI, platelet-derived endothelial cell growth factor (PD-ECGF), glucose oxidase, serum cholinesterase, aprotinin, amyloid precursor protein, inter-alpha trypsin inhibitor, antithrombin III, apo-lipoprotein species, Protein C, Protein S, a metabolite, an antibiotic, or a variant or fragment of any of the above.
 
127. The method according to embodiment 126 in which the fusion partner comprises or consists of a glucagon-like protein or analog thereof.
 
128. The method according to embodiment 127 in which the fusion partner comprises or consists of SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 51, or SEQ ID NO: 52.
 
129. The method according to any of embodiments 118 to 128 in which the desired protein comprises or consists of SEQ ID NO: 16.
 
130. The method according to any of embodiments 99 to 129 in which the host cell is cultured at a scale of at least 1 L.
 
131. The method according to embodiment 130 in which the host cell is cultured at a scale of at least 2 L.
 
132. The method according to embodiment 131 in which the host cell is cultured at a scale of at least 5 L.
 
133. The method according to embodiment 132 in which the host cell is cultured at a scale of at least 10 L.
 
134. The method according to embodiment 133 in which the host cell is cultured at a scale of at least 1000 L.
 
135. The method according to embodiment 134 in which the host cell is cultured at a scale of at least 5000 L.
 
136. The method according to any of embodiments 99 to 135 in which the desired protein is secreted from the fungal host cell.
 
137. The method according to embodiment 136 in which the desired protein results from an immature protein comprising a signal peptide.
 
138. The method according to embodiment 137 in which the signal peptide comprises or consists of SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 41 or SEQ ID NO: 42 or a signal peptide comprising the pentapeptide motif of SEQ ID NO: 20.
 
139. The method according to embodiment 138 in which the signal peptide comprises or consists of SEQ ID NO: 19.
 
140. The method according to embodiment 138 in which the signal peptide comprises or consists of SEQ ID NO: 24.
 
141. The method according to embodiment 138 in which the signal peptide comprises or consists of SEQ ID NO: 42.
 
142. The method according to any of embodiments 99 to 135 in which the desired protein is intracellular.
 
143. A desired protein (such as a heterologous protein) produced by the method according to any of embodiments 99 to 142.
 
144. The desired protein according to embodiment 143 for prophylaxis, therapy or diagnosis.
 
145. A composition, such as a pharmaceutical composition, comprising the desired protein according to embodiment 143 or 144 and a pharmaceutically acceptable carrier.
 
146. A method of treatment comprising administering the desired protein of embodiment 143 or 144 or the composition of embodiment 145 to a patient.
 
147. A method of preparing a fungal host cell according to any of embodiments 1 to 95 or a culture according to any of embodiments 96 to 98, the method comprising genetically modifying a (parent) fungal host cell to reduce the expression level and/or activity level of Gsh1 protein or homolog thereof.
 
148. The method according to embodiment 147, further comprising genetically modifying a (parent) fungal host cell to reduce the expression level and/or activity level of Not4 protein or homolog thereof.
 
149. Use of a means to reduce the expression level and/or activity level of Gsh1 protein or homolog thereof in a fungal host cell to increase the yield of a desired protein (such as a heterologous protein) from the fungal host cell, for example: by mutating or deleting the GSH1 gene, thus resulting in a mutated Gsh1 protein or homolog thereof or complete absence of Gsh1 protein or homolog thereof; by removing or changing the open reading frame of the gene; by mutating or changing control sequences of the GSH1 gene such as a promoter sequence and/or a terminator sequence; by blocking or reducing transcription of the GSH1 gene for example by introducing suitable interfering RNA such as antisense mRNA, by introducing, controlling or modifying suitable transcriptional activator genes or by introducing an agent which blocks activity level of Gsh1 protein or homolog thereof.
 
150. Use of a means to reduce the expression level and/or activity level of Gsh1 protein or homolog thereof and to reduce the activity level of Not4 protein or homolog thereof in a fungal host cell to increase the yield of a desired protein (such as a heterologous protein) from the fungal host cell, for example: by mutating or deleting the GSH1 gene and mutating or deleting the NOT4 gene, thus resulting in a mutated Gsh1 protein or homolog thereof or complete absence of Gsh1 protein or homolog thereof and resulting in a mutated Not4 protein or homolog thereof or complete absence of Not4 protein or homolog thereof; by removing or changing the open reading frame of the gene; by mutating or changing control sequences of the GSH1 and/or NOT4 gene such as a promoter sequence and/or a terminator sequence; by blocking or reducing transcription of the GSH1 and/or NOT4 gene for example by introducing suitable interfering RNA such as antisense mRNA; by introducing, controlling or modifying suitable transcriptional activator genes or by introducing an agent which blocks activity level of Gsh1 protein or homolog thereof and/or Not4 protein or homolog thereof.
 
151. A Gsh1 protein or homolog thereof, comprising at least 50% identity to SEQ ID NO: 2 and a mutation at a position corresponding to one or more positions selected from 47, 48, 49, 50, 51, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 409, 451, 452, 453, 454 and 455 of SEQ ID NO: 2.
 
152. The Gsh1 protein, or homolog thereof, according to embodiment 151 in which the position corresponds to R125 of SEQ ID NO: 2.
 
153. The Gsh1 protein, or homolog thereof, according to embodiment 151 or 152 in which the position corresponds to H409 of SEQ ID NO: 2.
 
154. The Gsh1 protein, or homolog thereof, according to any of embodiments 151 to 153 in which the position corresponds to P453 of SEQ ID NO: 2.
 
155. The Gsh1 protein, or homolog thereof, according to any of embodiments 151 to 154 in which the mutation is a substitution, preferably to a non-conserved amino acid.
 
156. The Gsh1 protein, or homolog thereof, according to any of embodiments 152 to 155 in which the mutation at a position corresponding to position R125 of SEQ ID NO: 2 is a substitution to A, C, D, E, F, G, H, I, L, M, N, P, Q, S, T, V, W or Y, preferably to C, D, E or G, more preferably to G.
 
157. The Gsh1 protein, or homolog thereof, according to any of embodiments 151 to 156 in which the mutation at a position corresponding to position R125 of SEQ ID NO: 2 is a substitution from a positively charged amino acid to an aliphatic, aromatic, hydrophobic, small, tiny, polar or negatively charged amino acid, preferably a negatively charged amino acid to a tiny amino acid.
 
158. The Gsh1 protein, or homolog thereof, according to any of embodiments 151 to 157 in which the mutation at a position corresponding to position D49 of SEQ ID NO: 2 is a substitution to A, C, F, G, H, I, K, L, M, N, P, Q, R, S, T, V, W or Y, preferably to H, K or R, more preferably to K or R.
 
159. The Gsh1 protein, or homolog thereof, according to any of embodiments 151 to 158 in which the mutation at a position corresponding to position 49 of SEQ ID NO: 2 is from a negatively charged amino acid to a positively charged amino acid.
 
160. The Gsh1 protein, or homolog thereof, according to any of embodiments 151 to 159 in which the mutation at a position corresponding to position H409 of SEQ ID NO: 2 is a substitution to A, C, D, E, F, G, I, K, L, M, N, P, Q, R, S, T, V, W or Y, preferably to A, I, L, V, M, F, W, Y, more preferably to A, I, L, V, most preferably to L.
 
161. The Gsh1 protein, or homolog thereof, according to any of embodiments 151 to 160 in which the mutation at a position corresponding to position H409 of SEQ ID NO: 2 is from an aromatic amino acid to an aliphatic amino acid.
 
162. The Gsh1 protein, or homolog thereof, according to any of embodiments 151 to 161 in which the mutation at a position corresponding to position P453 of SEQ ID NO: 2 is a substitution to A, C, D, E, F, G, H, I, K, L, M, N, Q, R, S, T, V, W or Y, preferably to A, I, L, V, M, F, W, Y, more preferably to A, I, L, V, most preferably to L.
 
163. The Gsh1 protein, or homolog thereof, according to any of embodiments 151 to 162 in which the mutation at a position corresponding to position P453 of SEQ ID NO: 2 is from an aromatic amino acid to an aliphatic amino acid.
 
164. The Gsh1 protein, or homolog thereof, according to any of embodiments 151 to 163 comprising or consisting of SEQ ID NO: 4.
 
           
         
       
    
     The invention is now described with reference to the following non-limiting examples: 
     EXAMPLES 
     Example 1: Mutation of the  Saccharomyces cerevisiae  GSH1 Gene 
       S. cerevisiae  DP9 has the genotype cirº MATa, leu2-3, leu2-112 ubc4 ura3 yap3::URA3 lys2 hsp150:LYS2 with PDI1, URA3 and Ylplac211 integrated at the PDI1 locus (Finnis et al, 2010, Microbial Cell Factories 9: 87). The inventors observed that  S. cerevisiae  DP9 (when transformed with an albumin-encoding plasmid) was able to produce recombinant human albumin at a higher yield than predecessor strains e.g.  S. cerevisiae  DB1. Characterisation of  S. cerevisiae  DP9 revealed a SNP in the GSH1 gene. To establish whether this SNP contributed to the improved protein yield of  S. cerevisiae  DP9, the SNP (A373G) was reverted to the wild-type (i.e. A at position 373) as described below. Consequently, the mutant Gsh1 protein (G125) was also reverted to wild-type (R125). The wild-type GSH1 gene and Gsh1 protein are provided in SEQ ID NO: 1 and SEQ ID NO: 2, respectively. The mutant (i.e. containing the SNP) GSH1 gene and Gsh1 protein are provided in SEQ ID NO: 3 and SEQ ID NO: 4, respectively. 
     The  S. cerevisiae  GSH1 gene is located on chromosome X. The SNP (A373G) in the mutant GSH1 gene was reverted to wild type by the process of integrating a fragment into the GSH1 locus, which changed base 373G to A, thus reverting the mutant Gsh1 protein (G at position 125) to wild-type Gsh1 protein (R at position 125). 
     This was achieved by first amplifying, by PCR, a suitable selection marker (KanMX) with DNA primers which included DNA sequences at their 5′ ends, identical to regions upstream of the GSH1 open reading frame. The PCR primers were MBP267 and MBP268. KanMX confers resistance to geneticin (G418). 
     
       
         
           
               
            
               
                 Primer MBP267: 
               
               
                 (SEQ ID NO: 29) 
               
               
                 5′-ATACTATTGTAATTCAAAAAAAAAAAGCGAATCTTCCCATGCCTGT 
               
               
                 TGCTGCTCTTGAATGGCGACAGCCTATTGCCCCAGTGTTCCCTCAACAA 
               
               
                 CCTTGCGTACGCTGCAGGTCG-3′ 
               
               
                   
               
               
                 Primer MBP268: 
               
               
                 (SEQ ID NO: 30) 
               
               
                 5′-ACAGTTGTAGTCACGTGCGCGCCATGCTGACTAATGGCAGCCGTCG 
               
               
                 TTGGGCAGAAGAGAATTAGTATGGTACAGGATACGCTAATTGCGCTCCA 
               
               
                 ACTACATCGATGAATTCGAGCTCG-3′ 
               
            
           
         
       
     
     PCR was performed to amplify the KanMX gene from the plasmid pDB5438 ( FIG. 2 ). Conditions were as follows: 100 ng plasmid pDB5438, 0.5 μM of each primer, 0.2 μM dNTPs, initial denaturation for 30 seconds at 98° C., then 35 cycles with 98° C. for 10 seconds, annealing at 62° C. for 30 seconds, extension at 72° C. for 2 minutes, followed by a final extension at 72° C. for 4 minutes, and cooling to 4° C., using an Applied Biosystems 2720 Thermal Cycler and a NEB Q5 Hot Start High-Fidelity DNA Polymerase PCR kit (M0493S), total reaction volume 50 μL, according to the manufacturer&#39;s instructions. 
     The product, 5′-GSH1 5′UTR-KanMX-GSH1 5′UTR-3′, was analysed by gel electrophoresis and was found to be of the expected size, approximately 1.7 kb. The amplified PCR product was purified. The purified product was used to transform a  S. cerevisiae  strain which was wild-type for GSH1 (i.e SEQ ID No: 1). Transformation was done using a Sigma Yeast Transformation kit according to the manufacturer&#39;s instructions, except that after the step where the transformation mix is centrifuged, the pellet was re-suspended in 0.5 mL YEPD medium, and then transferred to a shake flask containing 4.5 mL YEPD. YEPD (g/L): 10 g Bacto™ Yeast Extract Technical, 20 g Bacto™ Peptone, 20 g Glucose. 
     The shake flask was incubated for 16 hours at 30° C. with shaking (200 rpm). The culture was centrifuged at 3,000 revolutions per minute (rpm) for 5 minutes and the supernatant decanted. Then the pellet was washed in 1M sorbitol and then re-suspended in 0.5 ml 1M sorbitol. About 100 μl was then plated onto freshly prepared G418 agar plates (300 μg/ml G418 final concentration) and incubated face-down at 30° C. for four days. The G418 agar plates were prepared as follows: 0.17 g yeast nitrogen base (without (NH 4 ) 2 SO 4  and without amino acids), 0.1 g glutamic acid (monosodium salt, Sigma G-1626) and 0.069 g CSM-Leu powder were dissolved in 100 ml H 2 O (sterile water for irrigation—nonpyrogenic, hypotonic) and filter-sterilised. Then 1.5 g Bacto agar was added and the bottle was heated in a steamer for one hour and then cooled to 55° C. in a water bath. 0.6 ml 50 mg/ml Geneticin (G418) and 4 mL sterile 50% dextrose (w/v) were added and mixed. Aliquots of the mixture were poured into petri dishes to set. 
     Genomic DNA was extracted from G418 resistant transformants and used as a template in a second PCR, using primers MBP288 and MBP289, to amplify a 5′-GSH1 5′UTR-KanMX-GSH1 5′UTR-GSH1 ORF fragment (SEQ ID NO: 31) containing the GSH1 5′UTR with KanMX gene inserted, and the 5′ part of the GSH1 ORF (up to base 422) 
     
       
         
           
               
               
            
               
                   
                 Primer MBP288: 
               
               
                   
                 (SEQ ID NO: 32) 
               
               
                   
                 5′-GATTTTATCGGTCAAAGG-3′ 
               
               
                   
                   
               
               
                   
                 Primer MBP289: 
               
               
                   
                 (SEQ ID NO: 33) 
               
               
                   
                 5′-CTATCTTGTCTCGCATATTC-3′ 
               
            
           
         
       
     
     The PCR materials, method and conditions were as described above, except that 1 μl genomic DNA was used, the annealing temperature was 55° C. and the extension time was 3 minutes in each cycle and finally 7 minutes. The product was analysed by gel electrophoresis and was found to be of the expected size, approximately 2.9 kb. The amplified PCR products were purified using a QIAGEN QIAquick PCR Purification kit according to the manufacturer&#39;s instructions. The purified product was used to transform DP9 [pDB2305] ( FIG. 3 ) using the transformation method described above.  S. cerevisiae  DP9 is a strain containing the GSH1 SNP (A373G which results in R125G). pDB2305 is a plasmid for the expression of human albumin ( FIG. 3 ). The outgrowth and selection on G418 agar plates were as described above. Genomic DNA was extracted from resistant colonies, and PCR was used to amplify a 546 bp fragment that covered the region from 100 bp upstream of ORF to base 446 of ORF, using primers MBP290 and MBP292. The same PCR kit and conditions were used except the cycling steps were changed to an initial denaturation of 98° C. for 1 minute, followed by 35 cycles of 98° C. for 10 seconds, annealing at 61° C. for 20 seconds, and extension at 72° C. for 2.5 minutes and then a final extension at 72° C. for 7 minutes. 
     
       
         
           
               
               
            
               
                   
                 Primer MBP290: 
               
               
                   
                 (SEQ ID NO: 34) 
               
               
                   
                 5′-TCTCGAGTCACTTGTAGAAG-3′ 
               
               
                   
                   
               
               
                   
                 Primer MBP292: 
               
               
                   
                 (SEQ ID NO: 35) 
               
               
                   
                 5′-GAGCCCACATGCAAGTT-3′ 
               
            
           
         
       
     
     The products were cleaned using the Qiagen QIAquick 96 PCR Purification kit. A Life Technologies Big Dye Terminator v3.1 Cycle Sequencing kit was used for the sequencing of the products according to the manufacturer&#39;s instructions, using 50 μL total reaction volumes, with ˜50 ng of the cleaned products as template and 4 μL of 1 μM primer MBP291. The conditions were as following: Initial denaturation 96° C. 1 minute then 25 cycles with denaturation 96° C. for 10 seconds, annealing 50° C. for 5 seconds, elongation 60° C. for 4 minutes and finally cooling to 4° C. The sequencing reactions were precipitated and resuspended in HiDi (Applied Biosystems) and analysed on an Applied Biosystems 3130xl Genetic Analyser. 
     
       
         
           
               
               
            
               
                   
                 Primer MBP291: 
               
               
                   
                 (SEQ ID NO: 36) 
               
               
                   
                 5′-GTAGGGTGGTTTAGAGTATC-3′ 
               
            
           
         
       
     
     The sequencing analysis showed that one transformant had the wild type A at position 373 (R125), this strain was named PRG13 [pDB2305]. Two transformants still had the G at position 373 (G125), these strains were named PSG10 [pDB2305] and PSG11 [pDB2305]. These three transformants were cultured in a 48-well microtiter plate (MTP), containing 0.5 mL BMMD (0.17% (w/v) yeast nitrogen base without amino acid and ammonium sulphate (Difco), 37.8 mM ammonium sulphate, 36 mM citric acid, 126 mM disodium hydrogen orthophosphate pH6.5, 2% (w/v) glucose, adjusted to pH 6.5 with NaOH) in each well. The MTP was incubated at 30° C. in a humidity chamber with shaking (200 rpm) for 72 hours. Then 50 μL cell culture from each well was transferred into three wells in a new 48-well MTP containing 0.45 mL BMMD in each well. The new MTP was incubated at 30° C. in a humidity chamber with shaking (200 rpm) for 96 hours. 
     The supernatant was isolated by centrifugation and recombinant albumin productivity was determined by GP-HPLC analysis using a LC2010 HPLC system (Shimadzu) equipped with UV detection under Shimadzu VP7.3 client server software control. Injections of 75 μL were made onto a 7.8 mm id×300 mm length TSK G3000SWXL column (Tosoh Bioscience), with a 6.0 mm id×40 mm length TSK SW guard column (Tosoh Bioscience). Samples were chromatographed in 25 mM sodium phosphate, 100 mM sodium sulphate, 0.05% (w/v) sodium azide, pH 7.0 at 1 mL·min −1 , with a run time of 20 minutes. Samples were quantified by UV detection at 280 nm, by peak area, relative to a recombinant human albumin standard of known concentration (10 mg/mL) and corrected for their relative extinction coefficients. 
     As shown in Table 2, the presence of the SNP resulted in a 21% increase in average albumin yield. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Albumin productivity in PRG13 [pDB2305] compared with 
               
               
                 PSG10 [pDB2305] and PSG11 [pDB2305] 
               
            
           
           
               
               
               
            
               
                   
                   
                 GSH1 with SNP A373G 
               
               
                   
                 WT GSH1 (PRG13 
                 (PSG10 [pDB2305] and 
               
               
                   
                 [pDB2305]) 
                 PSG11 [pDB2305]) 
               
               
                   
               
               
                 Albumin (relative yield) 
                 100% ± 3.91% 
                 121% ± 5.58 
               
               
                   
               
               
                 P value (t-test): 8.89E−05 
               
            
           
         
       
     
     The work was repeated in a further  S. cerevisiae  strain. Briefly, the same transformation procedure was performed on  S. cerevisiae  strain BXP10 [pDB2244] ( FIG. 4 ), in order to revert the GSH1 SNP to wild-type. pDB2244 is a plasmid which expresses human albumin. the strains were grown in shake flask, approximately 10 mL of growth media in a 50 ml flask, incubated with shaking at 200 rpm at 30° C. The yield of albumin from a transformant still containing the SNP, i.e. BSG3 [pDB2244], was compared with the yield of albumin from a transformant with the SNP converted to wild-type i.e. BRG5 [pDB2244]. BXP10 has the genotype MATa, leu2-3, leu2-122, cant, prat, ubc4, ura3, yap3::URA3, lys2, hsp150::LYS2, and pmt1::URA3. 
     As shown by Table 3, the presence of the SNP resulted in a 68% increase in albumin yield (three replicates for each strain). 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Albumin productivity in BRG5 [pDB2244] and BSG3 [pDB2244] 
               
            
           
           
               
               
               
            
               
                   
                 BRG5 [pDB2244] 
                 BSG3 [pDB2244] 
               
               
                   
                 (WT GSH1) 
                 (GSH1 with SNP A373G 
               
               
                   
               
               
                 Albumin (relative yield) 
                 100% ± 7.84 
                 168% ± 9.45 
               
               
                   
               
               
                 P value (t-test): 0.001 
               
            
           
         
       
     
     Example 2: Deletion of the  S. cerevisiae  GSH1 Gene Enhanced the Production of Recombinant Protein 
     The GSH1 gene was deleted in the same two  S. cerevisiae  strains that were used in Example 1 for SNP reversion. The deletion was achieved by replacing the GSH1 gene with the marker KanMX. Consequently, the resultant strains were unable to produce any Gsh1 protein. In order to perform the deletion, the required DNA was ordered as a plasmid insert flanked by Acc65I restriction sites. The fragment of DNA consisted of the KanMX DNA flanked on the 5′ end by 300 bp immediately upstream to the GSH1 ORF and on the 3′ end by 300 bp immediately downstream to the GSH1 ORF (SEQ ID NO: 43). The plasmid was digested with Acc65I and the KanMX fragment purified from a Tris-acetate-EDTA (TAE) agarose gel using the QIAGEN gel extraction kit. This DNA was used to transform yeast strains DP9 [pDB2305] and BXP10 [pDB2244], where pDB2305 and pDB2244 are plasmids containing an expression cassette for human serum albumin. At the end of the transformation procedure the yeast cells were resuspended in YEPD media and grown overnight at 30° C. and 200 rpm. The following day they were plated on G418 plates (as described in Example 1), with L-glutathione added to 5 mM. Colonies were patched onto new plates (likewise with G418 and L-glutathione) and when the patches had grown, genomic DNA was extracted and PCRs performed using primers which would flank the junctions if the whole DNA fragment had integrated correctly. Three transformants were identified where GSH1 had been deleted in BXP10 (the transformants were named BDG1, BDG2 and BDG10) and one transformant where GSH1 had been deleted in DP9 (the transformant was named PDG14). These strains, together with the previously described strain with or without the SNP reversion, were cultured in 48 well plates in BMMD. The deletion strains were grown in wells supplemented with 5 mM L-glutathione and the other strains were cultured both with and without the L-glutathione. The supernatants were assayed by GP-HPLC to quantitate the expression levels of human serum albumin. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Albumin productivity in BXP10-derived strains: BRG5 [pDB2244] 
               
               
                 (WT GSH1), BSG3 [pDB2244] (SNP) and BDG1 [pDB2244], 
               
               
                 BDG2 [pDB2244] and BDG10 [pDB2244] (ΔGSH1) 
               
            
           
           
               
               
               
            
               
                   
                 Without L-glutathione 
                 With L-glutathione 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                   
                   
                 C 
                   
                   
                 F 
               
               
                   
                   
                   
                 BDG1 
                   
                   
                 BDG1 
               
               
                   
                   
                   
                 [pDB2244], 
                   
                   
                 [pDB2244], 
               
               
                   
                   
                 B 
                 BDG2 
                   
                 E 
                 BDG2 
               
               
                   
                 A 
                 BSG3 
                 [pDB2244] 
                 D 
                 BSG3 
                 [pDB2244] 
               
               
                   
                 BRG5 
                 [pDB2244] 
                 and BDG10 
                 BRG5 
                 [pDB2244] 
                 and BDG10 
               
               
                   
                 [pDB2244] 
                 (GSH1 
                 [pDB2244] 
                 [pDB2244] 
                 (GSH1 
                 [pDB2244] 
               
               
                 Strain(s) 
                 (WT GSH1) 
                 with SNP) 
                 (all ΔGSH1) 
                 (WT GSH1) 
                 with SNP) 
                 (all ΔGSH1) 
               
               
                   
               
               
                 Albumin 
                 100% ± 1.47 
                 132% ± 5.70 
                 (not tested) 
                 100% ± 6.67 
                 127% ± 6.84 
                 137% ± 9.74 
               
               
                 (relative 
               
               
                 yield) 
               
               
                   
               
               
                 (1 standard deviation) 
               
               
                 P value (t-test) deletion (grown with L-glutathione) compared to WT (grown without L-glutathione): 1.25E−08 (see Table 4, columns F and A) 
               
               
                 P value (t-test) deletion compared to WT (both grown with L-glutathione): 8.90E−05 (see table 4, columns F and D) 
               
            
           
         
       
     
     As shown in Table 4, deletion of GSH1 in BXP10 [pDB2244], resulted in an increase in albumin yield when compared to the strain with wild-type GSH1. In addition, as has also been shown in Example 1, the presence of the SNP in GSH1 increased albumin yield when compared with the strain containing wild-type GSH1. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Albumin productivity in DP9-derived strains: PRG13 [pDB2305] (WT 
               
               
                 GSH1), PSG10 [pDB2305] (GSH1 with SNP A373G) and PDG14 [pDB2305] (ΔGSH1) 
               
            
           
           
               
               
               
            
               
                   
                 Without L-glutathione 
                 With L-glutathione 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 A 
                 B 
                   
                 D 
                 E 
                   
               
               
                   
                 PRG13 
                 PSG10 
                 C 
                 PRG13 
                 PSG10 
                 F 
               
               
                   
                 [PDB2305] 
                 [PDB2305] 
                 PDG14 
                 [PDB2305] 
                 [PDB2305] 
                 PDG14 
               
               
                   
                 (WT 
                 (GSH1 
                 [PDB2305] 
                 (WT 
                 (GSH1 
                 [PDB2305] 
               
               
                   
                 GSH1) 
                 with SNP) 
                 (ΔGSH1) 
                 GSH1) 
                 with SNP) 
                 (ΔGSH1) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Albumin 
                 100% ± 5.30% 
                 130% ± 6.49% 
                 160% ± 8.63% 
                 100% ± 2.92% 
                 134% ± 5.47% 
                 160% ± 6.14% 
               
               
                 (relative 
               
               
                 yield) 
               
               
                   
               
               
                 (1 standard deviation) 
               
               
                 P value (t-test) deletion (grown with L-glutathione) compared to WT (grown without L-glutathione): 8.45895E−09 (see Table 5, columns F and A) 
               
               
                 P value (t-test) deletion compared to WT (both grown with L-glutathione): 1.02983E−05 (see Table 5, columns F and D) 
               
            
           
         
       
     
     As shown in Table 5, deletion of GSH1 in DP9 [pDB2305], resulted in an increase in albumin yield when compared to the strain with the wild-type GSH1, and when compared with the strain with the GSH1 with SNP. 
     Example 3: Mutation of the GSH1 Gene Improves Albumin Fermentation Yield at 10 L Scale 
     The BXP10 derived strains from Example 1 were grown at 10 liter scale in fermenters and the rate of specific cellular productivity (Y PXT ) yield was measured (Table 6). The fermentations were carried out in a manner similar to that described for Example 5. 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 Albumin productivity in 10 liter fermentations 
               
               
                 in BXP10 derived strains 
               
            
           
           
               
               
               
            
               
                   
                 BRG5 [pDB2244] 
                 BSG3 [pDB2244] 
               
               
                   
                 (WT GSH1) 
                 (GSH1 with SNP A373G) 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                 Albumin (relative 
                 100 
                 104.61 
               
               
                 yield, Y PXT ) (n = 6) 
               
               
                   
               
            
           
         
       
     
     An average increase of 4.6% was observed in the strain having GSH1 containing the SNP A373G (resulting in R125G), this was statistically significant. P-value=0.069 
     Example 4: The Positive Effect on Yield of Recombinant Protein from  S. cerevisiae  Provided by a Mutation in GSH1 is Further Enhanced by the Presence of a Mutation in NOT4 
     Previously (PCT/US2016/068239, incorporated herein by reference), it was identified that mutation of NOT4 (also known as MOT2) results in an increased yield of heterologous protein produced in a host strain. 
     In order to determine whether or not combining a mutation in NOT4 with a mutation in GSH1 further affects yield, one, both or neither mutations were complemented in host cells (by transformation with a plasmid containing a wild-type version of neither, one or both of the genes) resulting in a series of strains having phenotypes that approximate to: 
     (A) GSH1 containing SNP, and NOT4 containing SNP, 
     (B) GSH1 containing SNP, and wild-type NOT4, 
     (C) wild-type GSH1 and NOT4 containing SNP, and 
     (D) wild-type GSH1 and wild-type NOT4. 
     Heterologous protein yields were measured by GP-HPLC analysis of the supernatants of the cultures of the resulting strains. 
     To generate plasmids containing wild-type NOT4 and/or GSH1, PCRs were carried out with genomic DNA from yeast strain DB1. This strain has wild-type NOT4 and wild-type GSH1. Primer pairs (Table 7) were used to produce DNA containing the wild-type ORFs and upstream and downstream sequences of NOT4 and GSH1. The primers were designed to include restriction enzyme sites to allow cloning into the plasmid YCP50 ( FIG. 5 . and Rose et al., 1987, Gene, 60, 237-243). The PCRs were performed according to Table 8. 
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 PCR Primers 
               
            
           
           
               
               
               
               
            
               
                 Primer 
                 Sequence 
                 Restriction 
                 SEQ 
               
               
                 name 
                 (Underlined bases = restriction site) 
                 site 
                 ID NO: 
               
               
                   
               
               
                 MBP393 
                 5′-TATTAT GAATTC AAATGTTGAGCCCGAAGACG-3′ 
                 EcoRI 
                 37 
               
               
                   
               
               
                 MBP396 
                 5′-TATTAT AAGCTT AAATTAGCGAAGCAGGTTCC-3′ 
                 HindIII 
                 38 
               
               
                   
               
               
                 MBP397 
                 5′-TATTAT GCATGC CACGTATTCTTGTGCACACG-3′ 
                 SphI 
                 39 
               
               
                   
               
               
                 MBP406 
                 5′-TATTAT GTCGAC TACCACCTACACCAATAAGC-3′ 
                 SalI 
                 40 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 8 
               
             
            
               
                   
               
               
                 PCR conditions 
               
            
           
           
               
               
               
               
            
               
                 Target 
                   
                 Annealing 
                   
               
               
                 gene 
                 Primers 
                 temperature 
                 Genomic region amplified by PCR 
               
               
                   
               
               
                 NOT4 
                 MBP393 + 
                 64° C. 
                 385 bp upstream of ORF to 309 bp 
               
               
                   
                 MBP396 
                   
                 downstream 
               
               
                 GSH1 
                 MBP397 + 
                 62° C. 
                 596 bp upstream of ORF to 680 bp 
               
               
                   
                 MBP406 
                   
                 downstream 
               
               
                   
               
            
           
         
       
     
     The PCR conditions were as follows: 0.1 μg genomic DNA, 0.5 μM of each primer, 0.2 μM dNTPs, initial denaturation for 30 seconds at 98° C., then 35 cycles with 98° C. for 10 seconds, annealing at above temperature for 30 seconds, extension at 72° C. for 2 minutes, followed by a final extension at 72° C. for 4 minutes, and cooling to 4° C., using an Applied Biosystems 2720 Thermal Cycler and a NEB Q5 Hot Start High-Fidelity DNA Polymerase PCR kit (M0493S), total reaction volume 50 μL, according to the manufacturer&#39;s instructions. The products were analysed by gel electrophoresis and were found to be of the expected sizes, approximately 2.5 kb for NOT4 and approximately 3.3 kb for GSH1. The amplified PCR products were purified using a QIAGEN QIAquick PCR Purification kit according to the manufacturer&#39;s instructions. 
     Restriction enzyme digests were performed on the purified PCR products and on YCP50 plasmid. The restriction enzymes and buffers were from New England Biolabs (NEB) and the manufacturer&#39;s protocols were followed. The digests performed were: EcoRI+HindIII on the NOT4 PCR product, EcoRI+HindIII on YCP50, SphI+SalI on the GSH1 PCR product and SphI and SalI on YCP50. The buffer used was CutSmart buffer and the restriction enzymes were all the NEB High Fidelity (“HF”) enzymes (i.e. EcoRI-HF etc). The digests were incubated for about 1.5 hours at 37° C. The digests of PCR products were purified by QIAGEN QIAquick PCR Purification kit and the YCP50 DNA was purified from a TAE agarose gel, using the QIAGEN QIAquick gel extraction kit, according to the manufacturer&#39;s instructions. 
     Each of the digested and purified PCR products was ligated to the YCP50 DNA which had been cut with the same enzymes. The ligations were performed using the NEB Quick ligation kit (M2200S) according to the manufacturer&#39;s instructions and using a molar ratio of 3:1 for PCR product:YCP50. One microliter of each ligation reaction was then used to transform NEB 5-alpha competent (high efficiency)  E. coli  cells (M29871) according to the manufacturer&#39;s instructions and the cells were plated onto LB ampicillin. Overnight cultures were grown from resulting colonies and QIAGEN QIAprep spin minipreps were performed. Restriction enzyme digests were performed to identify plasmids in which the cloning appeared to have been successful. 
     The YCP50-NOT4 plasmid was then digested with SphI+SalI and the DNA purified from a TAE agarose gel, using the QIAGEN QIAquick gel extraction kit, according to the manufacturer&#39;s instructions. This DNA was ligated to GSH1 PCR product which had been digested with SphI+SalI and then purified using the QIAquick PCR purification kit. Again, the molar DNA ratio of insert to backbone was 3:1. NEB 5-alpha competent (high efficiency) cells were transformed (as above) and plasmid DNA prepared (as above). Correct plasmids were identified by restriction digests. 
     This resulted in three new plasmids: YCP50-NOT4, YCP50-GSH1 and YCP50-NOT4-GSH1. These, and YCP50 alone, were used to transform DYB7 ura3 [pDB2305] which contains plasmid pDB2305 for the expression of recombinant human serum albumin. DYB7 is described in Payne et al, (2008) Applied and Environmental Microbiology 74 (24) 7759-7766. The transformations were done using a Sigma Yeast Transformation kit according to the manufacturer&#39;s instructions, except after the step where the transformation mix is centrifuged, the pellet was re-suspended in 200 μl 1M sorbitol and then 100 μl was plated onto BMMD agar plates. The plates were incubated at 30° C. until colonies appeared. 
     Single colonies from each transformation were inoculated into wells of a 48 well microtiter plate, containing 0.5 ml BMMD per well. The plate was incubated at 30° C. and 200 rpm for 2 days and then an equal volume of 40% trehalose was mixed into each well and the plate stored at −80° C. At a later date, the plate was thawed and 50 μl transferred from each well to a well of a new plate containing 450 μl BMMD. This plate was incubated for 2 days at 30° C. and 200 rpm and then sub-cultured into another new plate (50 μl into 450 μl BMMD). This plate was incubated for 4 days. The plate was then centrifuged at 2000 rpm for 5 minutes and 200 μl supernatant from each was transferred to HPLC vials. The amounts of human serum albumin in the supernatants were quantitated by GP-HPLC as described in Example 1. 
     The new plasmids, YCP50-NOT4, YCP50-GSH1 and YCP50-NOT4-GSH1, were sequenced to confirm that they each contained the correct inserts. The sequencing was performed as described in the above examples, except that in this case 150 to 300 ng plasmid DNA was used for each reaction 
     The relative albumin yields, measured by GP-HPLC analysis of culture supernatants, are shown in Table 9 (below). 
     
       
         
           
               
             
               
                 TABLE 9 
               
             
            
               
                   
               
               
                 Albumin productivity in strains approximating 
               
               
                 to phenotypes containing combinations of GSH1 
               
               
                 (SNP or wild-type) and NOT4 (SNP or wild-type) 
               
            
           
           
               
               
            
               
                   
                 Plasmids used for complementation 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 B 
                 C 
                 D 
               
               
                   
                 A 
                 YCP50- 
                 YCP50- 
                 YCP50- 
               
               
                   
                 YCP50 
                 NOT4 
                 GSH1 
                 NOT4-GSH1 
               
               
                   
               
               
                 Resultant 
                 SNP 
                 SNP 
                 WT* 
                 WT* 
               
               
                 GSH1 status 
                   
                   
                   
                   
               
               
                 Resultant 
                 SNP 
                 WT* 
                 SNP 
                 WT* 
               
               
                 NOT4 status 
                   
                   
                   
                   
               
               
                 Albumin yield 
                 184% ± 4.88 
                 177% ± 4.45 
                 131% ± 4.59 
                 100% ± 4.88 
               
               
                 (relative) 
                   
                   
                   
                   
               
               
                 P value (t test) 
                 — 
                 1.10E−03 
                 4.20E−17 
                 1.87E−20 
               
               
                 compared to A 
               
               
                   
               
               
                 *Note that due to the method of construction of the strains analyzed in Table 9, the strains that contained a WT copy of the genes encoding GSH1 or NOT4 also contained the SNP versions (i.e. encoding Gsh1 R125G and Not4 F429I). The WT versions were on the plasmid and the SNP containing genes were in the genome. Due to complementation, the resultant phenotype approximates that of WT. 
               
            
           
         
       
     
     The yields are shown relative to (D), the strain in which there was complementation of both of the SNP-containing genes. It was seen that the NOT4 with SNP (C), resulted in a 31% increase in yield, the GSH1 with SNP (B) resulted in 77% increase in yield and the presence of both SNPs (A), resulted in 84% increase in yield. These complementation studies demonstrate that the GSH1 and NOT4 mutations positively affect albumin yield, and that when combined the yield is even further increased. 
     It is expected that such an increase in yield would also be observed at larger scale. This is because, Examples 1 and 2 demonstrate that mutation or deletion of GSH1 affects the yield of albumin produced from  S. cerevisiae  at small scale, Examples 3 and 5 demonstrate that this is also observed at 10 L scale and previous application PCT/US2016/068239 demonstrated that mutation or deletion of NOT4 affects the yield of albumin produced from  S. cerevisiae  at both small and 10 L scale. 
     Example 5: Mutation of the  S. cerevisiae  GSH1 Gene Enhanced Albumin Yield at 10 L Scale 
     The productivity of  S. cerevisiae  strains DYB7 ura3 [pDB2305/YCp50-NOT4], DYB7 ura3 [pDB2305/YCp50-GSH1] and DYB7 ura3 [pDB2305/YCp50-NOT4-GSH1] for recombinant protein expression were assessed by growth in 10 L fermenter (Wigley et al, (2007) Genetic Engineering News. 27 (2): 40-42). The fermentation was as described in Example 1 of WO97/33973 (incorporated herein by reference) using MW11D medium, except that Wonderware Supervisory Control and Data Acquisition software was used instead of MFCS, prior to use the fermenter vessel was also subjected to a citric acid wash, the trace element stock comprised Na 2 MoO 4 .2H 2 O instead of Na 2 MoO 4 .5H 2 O, the pH was adjusted to pH 6.2 with ammonia solution, initial introduction of sterile air into the vessel was at about 1.0 vvm (i.e. 1.0 liter) instead of 0.5 vvm, during the fermentation the airflow was increased in one step instead of two to maintain an airflow of approximately 1.0 vvm, the specific growth rate was approximately 0.06 h −1  and the exponential constant (K) was kept at 0.06. “vvm” means gas volume flow per unit of liquid volume per minute. 
     The relative yields are shown (grams of product per liter) in Table 10. 
     
       
         
           
               
             
               
                 TABLE 10 
               
             
            
               
                   
               
               
                 Productivity of albumin at 10 liter scale from DYB7 [pDB2305/YCp50- 
               
               
                 NOT4] and DYB7 [pDB2305/YCp50-NOT4-GSH1] 
               
            
           
           
               
               
               
               
            
               
                 Strain 
                 GSH1 status 
                 NOT4 status 
                 % g/L 
               
               
                   
               
               
                 DYB7 ura3 [pDB2305/YCp50- 
                 WT 
                 WT 
                 100 
               
               
                 NOT4-GSH1] 
                   
                   
                   
               
               
                 DYB7 ura3 [pDB2305/YCp50- 
                 SNP A373G 
                 WT 
                 112 
               
               
                 NOT4] 
               
               
                   
               
            
           
         
       
     
     The yield of albumin is increased in a strain that has GSH1 containing a SNP compared with that of a strain that has a GSH1 phenotype that approximates wild-type. 
     Example 6: Mutation or Deletion of the  Saccharomyces cerevisiae  GSH1 Gene Enhanced the Expression of an Albumin Variant and Deletion of GSH1 Enhanced the Expression of an Albumin Fusion Protein (Albumin-IL-1 Ra) and scFv (vHvL)-FLAG 
     The proteins being expressed in this example were (a) an albumin variant (SEQ ID NO: 45) containing 4 mutations relative to WT HSA (SEQ ID NO. 10), (b) IL-1 Ra genetically fused to the C-terminal of human serum albumin (SEQ ID NO: 47, “albumin-IL-1 Ra”) and (c) the scFv, FITC8 (Evans et al 2010, Protein Expression and Purification 73:113-124, including references 16 and 17, all incorporated herein by reference) with a FLAG tag (DYKDDDDK, SEQ ID NO: 50) at its C-terminal (SEQ ID NO: 49). 
     In preparation for expression of albumin-IL-1 Ra, plasmid pDB3936 ( FIG. 7 ) was cut with restriction enzymes Acc65I and BamHI and plasmid pDB5912 (containing an albumin-IL-1Ra expression cassette) was cut with enzymes NsiI and PvuI. A plasmid map for pDB5912 is provided in  FIG. 8 , the DNA sequence encoding albumin-IL-1Ra is shown in SEQ ID NO: 46. The restriction enzymes and buffers were from New England Biolabs. Both plasmid digests were purified using a Qiagen PCR purification kit following the manufacturer&#39;s instructions. 
     The 3 strains, PDG14 [pDB2305], PSG11 [pDB2305] and PRG13 [pDB2305], were cultured in shake flasks in YEPD media and sub-cultured 3 times in order to cure them of the plasmid (pDB2305). Dilutions of the final cultures were plated onto YEPD and then single colonies from these plates were patched onto YEPD. The YEPD patches were transferred to BMMD+5 mM L-glutathione plates and incubated at 30° C.; a lack of growth on BMMD+5 mM L-glutathione identified the cells which had been cured of plasmid. The cured yeast strains were each transformed, using the Sigma Yeast Transformation kit according to the manufacturer&#39;s instructions, with plasmid pDB5862 (for expression of the albumin variant) (a plasmid map for pDB5862 is provided in  FIG. 9 , the DNA sequence encoding the albumin variant is shown in SEQ ID NO. 44), pDB3029 (for expression of scFv (vHvL)-FLAG) (a plasmid map for pDB3029 is provided in  FIG. 9 , the DNA sequence encoding scFv-FLAG is shown in SEQ ID NO: 48), or with the purified restriction digests of pDB3936 and pDB5912 (for expression of albumin-IL-1 RA from the gap-repaired plasmid pDB3936:GR:pDB5912). The cells were plated onto BMMD and incubated for 5 days at 30° C. Six transformants of each strain were cultured in a 48 well MTP containing 0.5 ml BMMD with 5 mM L-glutathione per well. The plate was incubated for 48 hours at 30° C. and 200 rpm in a humidity chamber. This plate was then sub-cultured by transferring 50 μl of each culture into 450 μl BMMD with 5 mM L-glutathione in a new plate. This plate was incubated for 96 hours. 
     The supernatant was isolated by centrifugation and recombinant protein productivity (for albumin variant, albumin-IL-1Ra or ScFv) was determined by GP-HPLC, as in Example 1. 
     As shown in Table 11, the presence of the SNP (A373G) or deletion, resulted in an increase in yield of albumin variant. The yield was 15% higher in the strain containing the SNP in GSH1 (PSG11) and 23% higher in the strain containing the deletion of GSH1 (PDG14), compared to the strain with wild-type GSH1 (PRG13). 
     
       
         
           
               
             
               
                 TABLE 11 
               
             
            
               
                   
               
               
                 Albumin variant productivity in PRG13 [pDB5862], 
               
               
                 PSG11 [pDB5862] and PDG14 [pDB5862] 
               
            
           
           
               
               
               
               
            
               
                   
                 PRG13 
                 PSG11 
                 PPDG14 
               
               
                   
                 [pDB5862] 
                 [pDB5862] 
                 [pDB5862] 
               
               
                   
               
               
                 Albumin 
                 100% ± 19.74 
                 115% ± 18.63 
                 123% ± 20.34 
               
               
                 variant 
                   
                   
                   
               
               
                 (relative 
                   
                   
                   
               
               
                 yield) 
               
               
                   
               
               
                 P value (t-test) for SNP vs WT GSH1: P = 0.052 
               
               
                 P value (t-test) for deletion vs WT GSH1: P = 0.011 
               
            
           
         
       
     
     As shown in Table 12, the presence of the deletion resulted in an increase in yield of albumin-IL-1Ra. The yield was 14% higher in the strain containing the deletion (PDG14), compared to the strain with wild-type GSH1 (PRG13). 
     
       
         
           
               
             
               
                 TABLE 12 
               
             
            
               
                   
               
               
                 Albumin-IL-1Ra productivity in PRG13 [pDB3936:GR:pDB5912], PSG11 
               
               
                 [pDB3936:GR:pDB5912] and PDG14 [pDB3936:GR:pDB5912] 
               
            
           
           
               
               
               
               
            
               
                   
                 PRG13 
                 PSG11 
                 PPDG14 
               
               
                   
                 [pDB3936:GR:pDB5912] 
                 [pDB3936:GR:pDB5912] 
                 [pDB3936:GR:pDB5912] 
               
               
                   
               
               
                 Albumin- 
                 100% ± 20.69 
                 88% ± 15.75 
                 114 ± 17.37 
               
               
                 IL-1Ra 
                   
                   
                   
               
               
                 (relative 
                   
                   
                   
               
               
                 yield) 
               
               
                   
               
               
                 P value (t-test) for SNP vs WT GSH1: P = 0.11 
               
               
                 P value (t-test) for deletion vs WT GSH1: P = 0.049 
               
            
           
         
       
     
     As shown in Table 13, the presence of the deletion resulted in an increase in yield of ScFv-FLAG. The yield 38% higher in the strain containing the deletion of GSH1 (PDG14), compared to the strain with wild-type GSH1 (PRG13). 
     
       
         
           
               
             
               
                 TABLE 13 
               
             
            
               
                   
               
               
                 ScFv (vHvL)-FLAG productivity in PRG13 [pDB3029], PSG11 
               
               
                 [pDB3029] and PDG14 [pDB3029] 
               
            
           
           
               
               
               
               
            
               
                   
                 PRG13 
                 PSG11 
                 PDG14 
               
               
                   
                 [pDB3029] 
                 [pDB3029] 
                 [pDB3029] 
               
               
                   
               
               
                 ScFv (relative 
                 100% ± 19.40 
                 108% ± 19.77 
                 138% ± 22.32 
               
               
                 yield) 
               
               
                   
               
               
                 P value (t-test) for SNP vs WT GSH1: P = 0.33 
               
               
                 P value (t-test) for deletion vs WT GSH1: P = 0.0009