Abstract:
The present invention provides for functional chimeric gene regulatory units capable of driving strong and sustained heterologous gene expression.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application makes reference to and claims the benefit of priority of a Singapore patent application filed on 18 Jun. 2014, and duly assigned application number 10201403371T. The content of said application filed on 18 Jun. 2014 is incorporated herein by reference for all purposes, including an incorporation of any element or part of the description, claims or drawings not contained herein and referred to in Rule 20.5(a) of the PCT, pursuant to Rule 4.18 of the PCT. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention lies in the field of recombinant promoter variants capable of driving strong and sustained heterologous gene expression in in vitro and in vivo applications such as gene therapy and recombinant protein expression. 
       BACKGROUND OF THE INVENTION 
       [0003]    Strong promoters are desired for high level recombinant protein production, in order to provide large quantities of a desired recombinant protein permitting a wide range of possible uses including industrial processes, diagnosis and disease treatment. 
         [0004]    A typical promoter used for recombinant protein production contains a promoter element, an immediate upstream enhancer and if required other cis-acting regulatory elements. Optionally, transcription factors, which work in synergy to enhance transcription activity, are recruited to the site by specific sequence motifs. 
         [0005]    Increasing recombinant protein expression through improvements in transcription and through preventing promoter silencing is desirable for optimizing yield. In order to be able to provide functional proteins, mammalian proteins are often expressed in mammalian cell lines as these can ensure the required post-translational modifications, such as “native” mammalian glycosylation patterns and molecular folding steps. Thus, mammalian cells are an important host for the production of clinically relevant recombinant proteins. The most widely used approach for this purpose is to establish a cell line with an actively expressed recombinant gene stably integrated in its genome. Alternatively, proteins can be transiently produced in cells for a limited period of time without the necessity of recombinant gene integration. 
         [0006]    Chinese hamster ovary cells (CHO) cells have been the most commonly used mammalian host for large-scale commercial production of therapeutic proteins. The first CHO cell line was derived through single cell cloning in 1957. The cell line CHO-K1 was later derived from this ancestral cell line and it contains a slightly lower amount of DNA than the original CHO. Subsequently, another derivative of the original CHO cell line was mutagenized to yield CHO-DG44, a cell line with deletions of both dhfr alleles. While CHO cells are used in studies of genetics, toxicity screening, nutrition and gene expression, the most prominent use is recombinant protein expression. 
         [0007]    Process development using CHO cell lines focuses on achieving the maximum amount of active product. Optimization of the amount of active product can be achieved via increasing the specific productivity (i.e., the product per cell) and/or by cell line development. Cell line development may include both sub-cloning the cell line to select higher producing clones and use of gene amplification. 
         [0008]    Another way to achieve higher recombinant protein yields is to increase the cell yield (i.e., cells per volume) of the process. This may be accomplished through process development (e.g., batch, fed-batch, perfusion, etc.) and medium development. By increasing the cells per volume per day, higher levels of product may be produced. 
         [0009]    However, even though efficiency and output in recombinant protein production has substantially increased in recent years, there is still the need in the art for alternative methods that allow an even higher expression level. 
       SUMMARY OF THE INVENTION 
       [0010]    The inventors of the present application have found that said need can be met by novel chimeric gene regulatory units. 
         [0011]    In a first aspect the present invention therefore relates to an isolated nucleic acid molecule comprising a functional chimeric gene regulatory unit comprising (a) a functional enhancer nucleotide sequence, (b) a functional core promoter nucleotide sequence and (c) at least one nucleotide sequence encoding for an intron, wherein the enhancer nucleotide sequence is 5′ to the promoter nucleotide sequence and the intron nucleotide sequence is 3′ to the promoter sequence and wherein at least one nucleotide sequence of the enhancer nucleotide sequence, the promoter nucleotide sequence or the at least one nucleotide sequence encoding for the intron is derived from a different species than the other nucleotide sequences. 
         [0012]    In various embodiments, the isolated nucleic acid molecule further comprises at least one nucleotide sequence encoding for a polypeptide, peptide or RNA molecule, wherein said sequence is operably linked to the chimeric gene regulatory unit. The at least one nucleotide sequence encoding for a polypeptide, peptide or RNA molecule of interest may lie 3′ to the intron nucleotide sequence, preferably directly adjacent to the intron sequence. In various embodiments, where the nucleotide sequence encodes for a polypeptide of interest, said polypeptide of interest is a polypeptide chain of a naturally occurring or artificial immunoglobulin. In various embodiments, the polypeptide of interest may be an antibody or fragment thereof. The antibody may be a human or humanized antibody, or a fragment thereof. 
         [0013]    In various embodiments, the chimeric gene regulation unit has an increased resistance to transcriptional silencing. 
         [0014]    In various embodiments, the isolated nucleic acid molecule further comprises at least one nucleotide sequence encoding for a recognition site of a restriction endonuclease. The at least one nucleotide sequence encoding for a recognition site of a restriction endonuclease may be (i) 3′ to the enhancer nucleotide sequence and 5′ to the promoter nucleotide sequence or (ii) 3′ to the promoter nucleotide sequence and 5′ to the at least one nucleotide sequence encoding for an intron. 
         [0015]    In various embodiments, the enhancer sequence is derived from viruses, preferably from double-stranded DNA viruses. Said viruses may be of the group of Herpesviridae and Polyomaviridae, preferably of the group consisting of human cytomegalovirus, murine cytomegalovirus, and simian virus 40. 
         [0016]    In various embodiments, any one or more of the enhancer sequence, the promoter sequence and the intron sequence are derived from human cytomegalovirus, murine cytomegalovirus, simian virus 40, the human EF-1α gene, and the chicken β-actin gene. More preferably, the promoter may be derived from human cytomegalovirus, murine cytomegalovirus, simian virus 40, the human EF-1α gene, or the chicken β-actin gene, the enhancer may be derived from human cytomegalovirus, murine cytomegalovirus, or simian virus 40, and/or the intron sequence may be derived from human cytomegalovirus, the human EF-1α gene, or the chicken β-actin gene. 
         [0017]    In various embodiments, the enhancer sequence comprises, consists essentially of or consists of (i) a nucleotide sequence as set forth in any one of SEQ ID NO:1; SEQ ID NO:2; SEQ ID NO:3; or a complement thereof; or (ii) a nucleotide sequence that shares at least 75% sequence identity with a nucleotide sequence of (i) or a complement thereof. 
         [0018]    In various embodiments, the promoter sequence comprises, consists essentially of or consists of (i) a nucleotide sequence as set forth in any one of SEQ ID NO:4; SEQ ID NO:5; SEQ ID NO:6; SEQ ID NO:7; SEQ ID NO:8; or a complement thereof; or (ii) a nucleotide sequence that shares at least 75% sequence identity with a nucleotide sequence of (I) or a complement thereof. 
         [0019]    In various embodiments, the intron nucleotide sequence comprises, consists essentially of or consists of (i) a nucleotide sequence as set forth in any one of SEQ ID NO:9; SEQ ID NO:10; SEQ ID NO:11; or a complement thereof; or (ii) a nucleotide sequence that shares at least 75% sequence identity with a nucleotide sequence of (i) or a complement thereof. 
         [0020]    In various embodiments, the chimeric gene regulatory unit comprises, consists essentially of or consists of 
         [0000]    (1) the nucleotide sequences as set forth in SEQ ID NO:1; SEQ ID NO:4; and SEQ ID NO:11; or complements thereof;
 
(2) the nucleotide sequences as set forth in SEQ ID NO:2; SEQ ID NO:5; and SEQ ID NO:11; or complements thereof;
 
(3) the nucleotide sequences as set forth in SEQ ID NO:2; SEQ ID NO:4; and SEQ ID NO:11; or complements thereof;
 
(4) the nucleotide sequences as set forth in SEQ ID NO:2; SEQ ID NO:4; and SEQ ID NO:9; or complements thereof;
 
(5) the nucleotide sequences as set forth in SEQ ID NO:1; SEQ ID NO:5; and SEQ ID NO:11; or complements thereof;
 
(6) the nucleotide sequences as set forth in SEQ ID NO:1; SEQ ID NO:5; and SEQ ID NO:9; or complements thereof;
 
(7) the nucleotide sequences as set forth in SEQ ID NO:1; SEQ ID NO:7; and SEQ ID NO:11; or complements thereof;
 
(8) the nucleotide sequences as set forth in SEQ ID NO:1; SEQ ID NO:5; and SEQ ID NO:11; or complements thereof;
 
(9) the nucleotide sequences as set forth in SEQ ID NO:2; SEQ ID NO:7; and SEQ ID NO:9; or complements thereof;
 
(10) the nucleotide sequences as set forth in SEQ ID NO:2; SEQ ID NO:6; and SEQ ID NO:10; or complements thereof;
 
(11) the nucleotide sequences as set forth in SEQ ID NO:3; SEQ ID NO:7; and SEQ ID NO:10; or complements thereof;
 
(12) the nucleotide sequences as set forth in SEQ ID NO:1; SEQ ID NO:6; and SEQ ID NO:11; or complements thereof;
 
(13) the nucleotide sequences as set forth in SEQ ID NO:3; SEQ ID NO:5; and SEQ ID NO:10; or complements thereof;
 
(14) the nucleotide sequences as set forth in SEQ ID NO:1; SEQ ID NO:7; and SEQ ID NO:10; or complements thereof;
 
(15) the nucleotide sequences as set forth in SEQ ID NO:2; SEQ ID NO:6; and SEQ ID NO:11; or complements thereof;
 
(16) the nucleotide sequences as set forth in SEQ ID NO:2; SEQ ID NO:6; and SEQ ID NO:9; or complements thereof;
 
(17) the nucleotide sequences as set forth in SEQ ID NO:2; SEQ ID NO:7; and SEQ ID NO:11; or complements thereof;
 
(18) the nucleotide sequences as set forth in SEQ ID NO:1; SEQ ID NO:8; and SEQ ID NO:10; or complements thereof;
 
(19) the nucleotide sequences as set forth in SEQ ID NO:2; SEQ ID NO:5; and SEQ ID NO:10; or complements thereof;
 
(20) the nucleotide sequences as set forth in SEQ ID NO:3; SEQ ID NO:5; and SEQ ID NO:11; or complements thereof;
 
(21) the nucleotide sequences as set forth in SEQ ID NO:2; SEQ ID NO:5; and SEQ ID NO:9; or complements thereof;
 
(22) the nucleotide sequences as set forth in SEQ ID NO:2; SEQ ID NO:4; and SEQ ID NO:10; or complements thereof;
 
(23) the nucleotide sequences as set forth in SEQ ID NO:1; SEQ ID NO:7; and SEQ ID NO:11; or complements thereof;
 
(24) the nucleotide sequences as set forth in SEQ ID NO:2; SEQ ID NO:7; and SEQ ID NO:10; or complements thereof;
 
(25) the nucleotide sequences as set forth in SEQ ID NO:1; SEQ ID NO:5; and SEQ ID NO:10; or complements thereof; or
 
(26) a nucleotide sequence that shares at least 75% sequence identity with one nucleotide sequence of (1)-(25) or a complement thereof.
 
         [0021]    In various embodiments, the isolated nucleic acid molecule of the invention comprising the functional chimeric gene regulatory unit and the at least one nucleotide sequence encoding for a polypeptide, peptide or RNA molecule of interest has increased expression activity to express the polypeptide, peptide or RNA molecule of interest in CHO (Chinese Hamster Ovary) K1 or CHO DG44 cells compared to an isolated nucleic acid molecule comprising a naturally occurring gene regulatory unit and a nucleotide sequence encoding for the same polypeptide, peptide or RNA molecule of interest. The chimeric gene regulatory unit having increased expression activity in CHO K1 cells may comprise, consist essentially of or consist of (i) a nucleotide sequence as set forth in SEQ ID NO: 30, SEQ ID NO: 35, SEQ ID NO:59, SEQ ID NO:60, SEQ ID NO:62, SEQ ID NO: 64, SEQ ID NO: 65; or a complement thereof; or (ii) a nucleotide sequence that shares at least 75% sequence identity with a nucleotide sequence of (i) or a complement thereof. The chimeric gene regulatory unit having increased expression activity in CHO DG44 cells may comprise, consist essentially of or consist of (i) a nucleotide sequence as set forth in SEQ ID Nos. 34, 36, 37, 45, 47-52, 56, 57, 59-62, 64-67, 71 or a complement thereof; or (ii) a nucleotide sequence that shares at least 75% sequence identity with a nucleotide sequence of (i) or a complement thereof. 
         [0022]    In various embodiments, the promoter comprises at least one binding site for a transcription factor. The transcription factor may be specificity protein 1 (Sp1) transcription factor. The Sp1 transcription factor may comprise, consist essentially of or consist of a polypeptide sequence as set forth in any one of SEQ ID NO:74 and SEQ ID NO:75, or a fragment thereof. In various embodiments, the at least one binding site for a transcription factor comprises, consists essentially of or consists of the nucleotide sequence set forth in SEQ ID NO:76 (5′-(G/T)GGGCGG(G/A)(G/A)(C/T)-3′). 
         [0023]    In another aspect, the present invention relates to a vector comprising the isolated nucleic acid molecule as described herein, preferably a plasmid. 
         [0024]    In still another aspect, the present invention is also directed to a host cell comprising the isolated nucleic acid molecule or the vector as described herein. The host cell may be a eukaryotic cell, such as a CHO cell, preferably a CHO K1 cell or a CHO DG44 cell. 
         [0025]    Another aspect of the invention is directed to the use of the isolated nucleic acid molecule of the invention for facilitating or enhancing the expression of a polypeptide, peptide or RNA of interest, wherein said isolated nucleic acid molecule comprises a nucleotide sequence encoding the polypeptide, peptide or RNA of interest, wherein said nucleotide sequence encoding the polypeptide, peptide or RNA of interest is operably linked to the chimeric gene regulatory unit of the isolated nucleic acid molecule. 
         [0026]    Still another aspect is related to a method of producing a polypeptide, peptide or RNA of interest, comprising: 
         [0027]    (i) providing the isolated nucleic acid molecule as described herein, wherein said isolated nucleic acid molecule comprises a nucleotide sequence encoding the polypeptide, peptide or RNA of interest, said nucleotide sequence encoding the polypeptide, peptide or RNA of interest being operably linked to the chimeric gene regulatory unit of the isolated nucleic acid molecule; and 
         [0028]    (ii) producing the polypeptide, peptide or RNA of interest by in vitro transcription and translation or in a suitable host cell under conditions that allow production of the polypeptide, peptide or RNA of interest. In such methods, the host cell may be a eukaryotic cell, such as a CHO cell, preferably a CHO K1 cell or a CHO DG44 cell. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    The invention will be better understood with reference to the detailed description when considered in conjunction with the non-limiting examples and the accompanying drawings. 
           [0030]      FIG. 1  shows a schematic overview of the design of the chimeric gene regulatory unit. Five natural gene regulatory units occurring upstream of the human cytomegalovirus immediate early gene (hCMV), of the murine cytomegalovirus immediate early gene (mCMV), the simian virus 40 (SV40), the human elongation factor-1α gene (hEF-1α) and the chicken β-actin gene (cA) were dissected into enhancers (E), core promoters (CP) and introns (I). These enhancers, core promoters, and introns from different sources were then combined to generate fifty-seven new enhancer-core promoter and enhancer-core promoter-intron combinations, referred to as chimeric gene regulatory units or hybrid promoters. 
           [0031]      FIG. 2  shows a schematic representation of monoclonal antibody expressing vectors for comparison of different chimeric promoters. (A) Antibody expression vector for comparison of chimeric promoters in CHO K1 cells. (B) Antibody expression vector for comparison of chimeric promoters in CHO DG44 cells. ChiP: chimeric gene regulatory unit; LC: antibody light chain encoding sequence; HC: antibody heavy chain encoding sequence; Zeo: zeocin encoding sequence; DHFR: dihydrofolate reductase encoding sequence; IRESwt: wild-type encephalomyocarditis virus internal ribosome entry site; mIRES, mutated IRES with reduced translation efficiency; pA: polyadenlyation signal. 
           [0032]      FIG. 3  shows the results of the comparison of the newly generated chimeric gene regulatory units according to  FIG. 2  and Table 2 with the wild type promoters for expression level in stably transfected CHO K1 (A) and CHO DG44 (B) cells. Stably transfected pools were generated by transfection of CHO K1/CHO DG44 cells with monoclonal antibody (mAb) expressing vectors containing different chimeric promoters and selection of stable transfectants using zeocin. Antibody titers of stably transfected pools were determined in shake flask batch cultures. The black bar represents the titer from the strongest wild type promoter. Seven hybrid promoters exhibited higher recombinant protein production than any wild type promoters in CHO K1 cells. 21 hybrid promoters exhibit higher expression than any wild type promoters in CHO DG44 cells. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0033]    The following detailed description refers to, by way of illustration, specific details and embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized and structural, and logical changes may be made without departing from the scope of the invention. The various embodiments are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments. 
         [0034]    Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present document, including definitions, will control. 
         [0035]    The object of the present invention is to provide novel chimeric gene regulatory units for high level expression of a molecule of interest. 
         [0036]    In one first aspect, the present invention relates to an isolated nucleic acid molecule comprising a functional chimeric gene regulatory unit comprising (a) a functional enhancer nucleotide sequence, (b) a functional promoter nucleotide sequence and (c) at least one nucleotide sequence encoding for an intron, wherein the enhancer nucleotide sequence is 5′ to the promoter nucleotide sequence and the intron nucleotide sequence is 3′ to the promoter sequence and wherein at least one nucleotide sequence of the enhancer nucleotide sequence, the promoter nucleotide sequence or the at least one nucleotide sequence encoding for the intron is derived from a different species than the other nucleotide sequences. 
         [0037]    As used herein the term “functional” refers to an entity, which possesses either the native biological activity of the naturally-occurring entity of its type, or any specific desired activity, for example in case of a promoter as judged by its ability to initiate gene transcription. 
         [0038]    As used herein the term “isolated nucleic acid molecule” relates to nucleic acid molecules that may appear independent of their natural genetic context and/or background and are preferably separated from other nucleic acids or cellular components. The separation may occur by purification, for which various techniques are known in the art. 
         [0039]    The term “nucleic acid molecule” refers to the phosphate ester polymeric form of ribonucleosides (adenosine, guanosine, uridine or cytidine; “RNA molecules”) or deoxyribonucleosides (deoxyadenosine, deoxyguanosine, deoxythymidine, or deoxycytidine; “DNA molecules”), any phosphoester analogs thereof, such as phosphorothioates and thioesters, in either single stranded form, or as a double-stranded helix as well as artificial nucleic acid analogs such as peptide nucleic acid, morpholino- and locked nucleic acid, as well as glycol nucleic acid and threose nucleic acid. Each of these artificial nucleic acid analogs is distinguished from naturally occurring DNA or RNA by changes to the backbone of the molecule. In preferred embodiments the isolated nucleic acid molecule is a DNA molecule. 
         [0040]    “At least one”, as used herein, relates to one or more, in particular 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more. 
         [0041]    The articles “a” and “an” are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, “an element” means at least one element and can include more than one element. 
         [0042]    The term “sequence”, as used herein in relation to nucleic acids, relates to the primary sequence of nucleic acid molecules. 
         [0043]    As used herein the term “functional chimeric gene regulatory unit” or “hybrid promoter” refers to the combination of enhancer, core promoter and at least one intron as described herein. 
         [0044]    As used herein the term “chimeric” or “hybrid” refers to the fact that different elements of the regulatory unit are derived from different genes, i.e. in nature the combinations of elements of the regulatory unit as described herein do not exist. This may be achieved by using at least one of the elements from a different species and combining it with the other elements of the regulatory unit. At least one of the enhancer, the core promoter and the intron is thus heterologous with respect to at least one of the other two. 
         [0045]    As used herein the term “functional enhancer” refers to a short region of DNA that can activate transcription (of a gene), for example by being capable of binding proteins (activators). 
         [0046]    In general the term “promoter” refers to a region of DNA that initiates transcription of a particular gene. 
         [0047]    As used herein the term “functional promoter” or “core promoter” refers to the core region in a promoter, which is the minimal portion of the promoter required to properly initiate gene transcription. 
         [0048]    As used herein the term “intron” refers to a nucleotide sequence within a gene that is removed by RNA splicing during maturation of the final RNA product. The term intron refers to both the DNA sequence within a gene and the corresponding sequence in RNA transcripts. Sequences that are joined together in the final mature RNA after RNA splicing are exons. 
         [0049]    The term “5′” as used herein refers to the directionality, i.e., the end-to-end chemical orientation of a single strand of nucleic acid. The chemical convention of naming carbon atoms in the nucleotide sugar-ring numerically gives rise to a 5-end and a 3-end. The relative positions of structures along a strand of nucleic acid, including genes and various protein binding sites, are usually noted as being either upstream (towards the 5-end) or downstream (towards the 3-end). This naming convention is important because nucleic acids can only be synthesized in vivo in the 5-to-3′direction, as the polymerase that assembles new strands only attaches new nucleotides to the 3-hydroxyl (—OH) group, via a phosphodiester bond. 
         [0050]    In various embodiments, the isolated nucleic acid molecule further comprises at least one nucleotide sequence encoding for a peptide, polypeptide or RNA molecule of interest. Said molecules of interest are those to be expressed using the novel chimeric gene regulatory units if high level expression is desired. Preferably, it is a recombinant polypeptide or protein. 
         [0051]    As used herein, the term “peptide” relates to two or more amino acids linked by a peptide bond and thus includes dipeptides, oligopeptides, and polypeptides. 
         [0052]    The term “polypeptide”, as used herein, refers to a long, continuous peptide chain, preferably of at least 50 amino acids in length. 
         [0053]    The term “protein”, as used herein, relates to one or more polypeptides arranged in a biologically functional way. A protein may consist of more than one polypeptide chains, such as an antibody, which consists of two light chains and two heavy chains, with each of the chains being a polypeptide. A protein may be bound to ligands such as coenzymes and cofactors or to another protein or other macromolecule. 
         [0054]    In various embodiments, said sequence encoding the molecule of interest is operably linked to the chimeric gene regulatory unit. In preferred embodiments, the at least one nucleotide sequence encoding for a molecule of interest lies 3′ (downstream) relative to the intron nucleotide sequence. In more preferred embodiments, the at least one nucleotide sequence encoding a molecule of interest lies directly adjacent to the intron sequence. 
         [0055]    “Directly adjacent” means that the intron sequence and the coding sequence are directly linked by a phosphodiester bond and that no linker nucleotide sequence is interposed between the two elements. 
         [0056]    As used herein the term “operably linked” means associated in such a way that the chimeric gene regulatory unit may control expression of the molecule of interest. 
         [0057]    It is advantageous that the at least one nucleotide sequence encoding for a molecule of interest lies directly adjacent to the intron sequence, because this increases the chances of correct and high level expression. 
         [0058]    In various embodiments, where the at least one nucleotide sequence encoding for a molecule of interest encodes for a polypeptide of interest, said polypeptide is a polypeptide chain of a naturally occurring or artificial immunoglobulin. In preferred embodiments, the polypeptide of interest is a protein and the protein is an antibody. In more preferred embodiments, the antibody is a human or humanized antibody, or a fragment thereof. It is understood that in such embodiments, wherein expression of an immunoglobulin, specifically an antibody is desired, the isolated nucleic acid molecules comprises nucleotide sequences that encode for more than one polypeptide. For example, in case antibody expression is desired, the isolated nucleic acid molecule may comprise two nucleic acid sequences encoding for a polypeptide of interest, namely one sequence encoding the heavy chain and one sequence encoding the light chain. In such embodiments, the different coding sequences may be directly linked or may be separated by linker nucleotide sequences. Said linker nucleotide sequences may be functional in that they allow ribosomal binding and may thus for example include internal ribosomal entry sites (IRES). 
         [0059]    As used herein and in line with the above, the term “immunoglobulin” refers to a protein consisting of one or more polypeptides substantially encoded by immunoglobulin genes. 
         [0060]    In various embodiments, the chimeric gene regulation unit has an increased resistance to transcriptional silencing. 
         [0061]    The term “transcriptional silencing” refers to any mechanism, whereby gene expression is down-regulated on transcriptional level, e.g. via DNA methylation, histone modifications and chromatin remodeling, which make the DNA permanently inaccessible for future transcription. 
         [0062]    It is advantageous if the chimeric gene regulation unit has an increased resistance to transcriptional silencing, as this will result in higher overall yields of expressed product. 
         [0063]    In various embodiments, the isolated nucleic acid molecule further comprises at least one nucleotide sequence encoding for a recognition site of a restriction endonuclease. In preferred embodiments, said at least one nucleotide sequence encoding for a recognition site of a restriction endonuclease is 3′ to the enhancer nucleotide sequence and 5′ to the promoter nucleotide sequence. Alternatively, in various preferred embodiments, said nucleotide sequence encoding for a recognition site of a restriction endonuclease is 3′ to the promoter nucleotide sequence and 5′ to the at least one nucleotide sequence encoding for an intron. This location allows separating and combining the different elements of the regulatory unit in a specific manner, e.g. linking enhancer, promoter and intron sequences. 
         [0064]    As used herein, the term “restriction endonuclease” is intended to mean an enzyme that recognizes a specific nucleotide sequence in a nucleic acid and cleaves the nucleic acid. A restriction endonuclease can recognize a sequence that is, for example, 4, 5, 6, 7 or more nucleotides long. A restriction endonuclease can recognize more than one sequence, for example, two or more variants of a degenerate sequence that includes one of two or more different nucleotides at a particular position. Alternatively, a restriction endonuclease can be specific for a single recognition sequence. 
         [0065]    As used herein, the term “recognition site” is intended to mean a portion of the nucleic acid having a nucleotide sequence that specifically binds to a particular binding moiety such as a restriction endonuclease, more specifically the substrate recognition and binding site of a restriction endonuclease. Typically, a restriction endonuclease recognition site is cleaved by a restriction endonuclease. 
         [0066]    In various embodiments, the enhancer sequence is derived from viruses. In preferred embodiments, the enhancer sequence is derived from double-stranded DNA viruses. In more preferred embodiments, the enhancer sequence is derived from viruses consisting of the group of Herpesviridae and Polyomaviridae. In still more preferred embodiments, the enhancer sequence is derived from the group consisting of human cytomegalovirus; murine cytomegalovirus; and simian virus 40. 
         [0067]    Cytomegalovirus is a viral genus of the Herpesviridae abbreviated as CMV. The species that infects humans is commonly known as human CMV (hCMV). Other CMV viruses such as murine cytomegalovirus in mice are found in several mammal species, but species isolated from animals differ from hCMV in terms of genomic structure. 
         [0068]    Simian virus 40 (SV40) is a polyomavirus that is found in both monkeys and humans. 
         [0069]    In various embodiments, the enhancer sequence comprises, consists essentially of or consists of (i) a nucleotide sequence as set forth in any one of SEQ ID NO:1; SEQ ID NO:2; SEQ ID NO:3; or a complement thereof; or (ii) a nucleotide sequence that shares at least 75%, 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 97.5%, 98.0%, 98.5%, 99.0%, or 99.5% sequence identity with a nucleotide sequence of (i) or a complement thereof. 
         [0070]    “Complement”, as used herein, relates to a nucleic acid molecule which is complementary to another nucleic acid molecule when both nucleic acid molecules are aligned antiparallel to each other in that essentially all nucleotides of either of the nucleic acid molecules form Watson-Crick base pairs with the corresponding nucleotides on the other molecule. In various embodiments, the complements are full complements in that each nucleotide of the respective molecule or sequence forms a Watson-Crick base pair with a corresponding nucleotide on the other strand. 
         [0071]    The term “sequence identity,” as used herein, is generally expressed as a percentage and refers to the percent of amino acid residues or nucleotides, as appropriate, that are identical as between two sequences when optimally aligned. For the purposes of this invention, sequence identity means the sequence identity determined using the well-known Basic Local Alignment Search Tool (BLAST), which is publicly available through the National Cancer Institute/National Institutes of Health (Bethesda, Md.) and has been described in printed publications (see, e.g., Altschul et al., J. Mol. Biol, 215(3), 403-10 (1990)). 
         [0072]    In various embodiments, the sequence of the core promoter is derived from the group consisting of human cytomegalovirus; murine cytomegalovirus; simian virus 40; the human EF-1α gene promoter; and the chicken β-actin gene promoter. 
         [0073]    Elongation factor 1-alpha 1 (EF-1α) is a protein that in humans is encoded by the EEF1A1 gene. This gene encodes an isoform of the alpha subunit of the elongation factor-1 complex, which is responsible for the enzymatic delivery of aminoacyl tRNAs to the ribosome. 
         [0074]    In various embodiments, the core promoter sequence comprises, consists essentially of or consists of (i) a nucleotide sequence as set forth in any one of SEQ ID NO:4; SEQ ID NO:5; SEQ ID NO:6; SEQ ID NO:7; SEQ ID NO:8; or a complement thereof; or (ii) a nucleotide sequence that shares at least 75%, 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 97.5%, 98.0%, 98.5%, 99.0%, or 99.5% sequence identity with a nucleotide sequence of (i) or a complement thereof. 
         [0075]    In various embodiments, the intron nucleotide sequence is selected from a sequence derived from the group consisting of human cytomegalovirus; the human EF-1α gene; and the chicken β-actin gene. 
         [0076]    In various embodiments, the intron nucleotide sequence comprises, consists essentially of or consists of (i) a nucleotide sequence as set forth in any one of SEQ ID NO:9; SEQ ID NO:10; SEQ ID NO:11; or a complement thereof; (ii) a nucleotide sequence that shares at least 75%, 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 97.5%, 98.0%, 98.5%, 99.0%, or 99.5% sequence identity with a nucleotide sequence of (i) or a complement thereof. 
         [0077]    The above elements may be combined, such that the chimeric gene regulatory unit comprises, consists essentially of or consists of 
         [0000]    (1) the nucleotide sequences as set forth in SEQ ID NO:1; SEQ ID NO:4; and SEQ ID NO:11; or complements thereof;
 
(2) the nucleotide sequences as set forth in SEQ ID NO:2; SEQ ID NO:5; and SEQ ID NO:11; or complements thereof;
 
(3) the nucleotide sequences as set forth in SEQ ID NO:2; SEQ ID NO:4; and SEQ ID NO:11; or complements thereof;
 
(4) the nucleotide sequences as set forth in SEQ ID NO:2; SEQ ID NO:4; and SEQ ID NO:9; or complements thereof;
 
(5) the nucleotide sequences as set forth in SEQ ID NO:1; SEQ ID NO:5; and SEQ ID NO:11; or complements thereof;
 
(6) the nucleotide sequences as set forth in SEQ ID NO:1; SEQ ID NO:5; and SEQ ID NO:9; or complements thereof;
 
(7) the nucleotide sequences as set forth in SEQ ID NO:1; SEQ ID NO:7; and SEQ ID NO:11; or complements thereof; or
 
(8) a nucleotide sequence that shares at least 75%, 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 97.5%, 98.0%, 98.5%, 99.0%, or 99.5% sequence identity with one nucleotide sequence of (1)-(7) or a complement thereof.
 
         [0078]    Such chimeric gene regulatory units are advantageous as it was surprisingly found that they exhibit higher recombinant protein production levels in CHO KG1 cells compared with wild type gene regulatory units or different chimeric gene regulatory units. 
         [0079]    The term “wild-type” (WT), as used herein, refers to the typical, most common or conventional form as it occurs in nature. 
         [0080]    In various embodiments, the isolated nucleic acid molecule of the invention comprising the functional chimeric gene regulatory unit and the at least one nucleotide sequence encoding for a molecule of interest has increased expression activity in that it expresses a molecule of interest in Chinese Hamster Ovary (CHO) K1 cells in higher levels relative to an isolated nucleic acid molecule comprising a naturally occurring gene regulatory unit and a nucleotide sequence encoding for the same molecule of interest. In preferred embodiments, the increased expression activity of the functional chimeric gene regulatory unit is at least 1.1-fold, 1.15-fold, 1.2-fold, 1.4-fold, 1.5-fold, 1.6-fold or 1.75-fold higher compared to the naturally occurring gene regulatory unit. 
         [0081]    CHO cells are advantageous due to their ability to produce glycoproteins with post-translational modifications compatible to humans, their refractory nature to human viruses, the availability of well-established gene amplification systems for CHO cells coupled with the cells ability to adapt and grow in serum-free suspension culture. These characteristics render the CHO cells ideal for large scale high-titer cultures in the industry. 
         [0082]    In various embodiments, the chimeric gene regulatory unit comprises, consists essentially of or consists of (i) a nucleotide sequence as set forth in SEQ ID NO: 30, SEQ ID NO: 35, SEQ ID NO:59, SEQ ID NO:60, SEQ ID NO:62, SEQ ID NO: 64, SEQ ID NO: 65 or a complement thereof; or (ii) a nucleotide sequence that shares at least 75%, 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 97.5%, 98.0%, 98.5%, 99.0%, or 99.5% sequence identity with a nucleotide sequence of (i) or a complement thereof. It was found that said constructs provide for increased expression activity in CHO K1 cells. Particularly preferred is a chimeric gene regulatory unit that comprises, consists essentially of or consists of the nucleotide sequence as set forth in SEQ ID NO:35 or a nucleotide sequence that shares at least 75%, 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 97.5%, 98.0%, 98.5%, 99.0%, or 99.5% sequence identity with said nucleotide sequence of SEQ ID NO:35 or the respective complements of these sequences. It was found that said sequence is particularly advantageous—even though it may not provide the highest titer—because the time used to generate stably transfected cell pools with said chimeric gene regulatory unit is significantly shorter—e.g. three weeks instead of two weeks—compared to the chimeric promoters set forth in SEQ ID Nos. 30, 59, 60, 62, 64 and 65. 
         [0083]    In various other embodiments, the chimeric gene regulatory unit comprises, consists essentially of or consists of 
         [0000]    (1) the nucleotide sequences as set forth in SEQ ID NO:2; SEQ ID NO:4; and SEQ ID NO:11; or complements thereof;
 
(2) the nucleotide sequences as set forth in SEQ ID NO:2; SEQ ID NO:5; and SEQ ID NO:11; or complements thereof;
 
(3) the nucleotide sequences as set forth in SEQ ID NO:1; SEQ ID NO:5; and SEQ ID NO:11; or complements thereof;
 
(4) the nucleotide sequences as set forth in SEQ ID NO:2; SEQ ID NO:7; and SEQ ID NO:9; or complements thereof;
 
(5) the nucleotide sequences as set forth in SEQ ID NO:2; SEQ ID NO:6; and SEQ ID NO:10; or complements thereof;
 
(6) the nucleotide sequences as set forth in SEQ ID NO:3; SEQ ID NO:7; and SEQ ID NO:10; or complements thereof;
 
(7) the nucleotide sequences as set forth in SEQ ID NO:1; SEQ ID NO:6; and SEQ ID NO:11; or complements thereof;
 
(8) the nucleotide sequences as set forth in SEQ ID NO:3; SEQ ID NO:5; and SEQ ID NO:10; or complements thereof;
 
(9) the nucleotide sequences as set forth in SEQ ID NO:1; SEQ ID NO:7; and SEQ ID NO:10; or complements thereof;
 
(10) the nucleotide sequences as set forth in SEQ ID NO:2; SEQ ID NO:6; and SEQ ID NO:11; or complements thereof;
 
(11) the nucleotide sequences as set forth in SEQ ID NO:2; SEQ ID NO:6; and SEQ ID NO:9; or complements thereof;
 
(12) the nucleotide sequences as set forth in SEQ ID NO:2; SEQ ID NO:7; and SEQ ID NO:11; or complements thereof;
 
(13) the nucleotide sequences as set forth in SEQ ID NO:1; SEQ ID NO:8; and SEQ ID NO:10; or complements thereof;
 
(14) the nucleotide sequences as set forth in SEQ ID NO:2; SEQ ID NO:5; and SEQ ID NO:10; or complements thereof;
 
(15) the nucleotide sequences as set forth in SEQ ID NO:3; SEQ ID NO:5; and SEQ ID NO:11; or complements thereof;
 
(16) the nucleotide sequences as set forth in SEQ ID NO:1; SEQ ID NO:4; and SEQ ID NO:11; or complements thereof;
 
(17) the nucleotide sequences as set forth in SEQ ID NO:2; SEQ ID NO:5; and SEQ ID NO:9; or complements thereof;
 
(18) the nucleotide sequences as set forth in SEQ ID NO:2; SEQ ID NO:4; and SEQ ID NO:10; or complements thereof;
 
(19) the nucleotide sequences as set forth in SEQ ID NO:1; SEQ ID NO:7; and SEQ ID NO:11; or complements thereof;
 
(20) the nucleotide sequences as set forth in SEQ ID NO:2; SEQ ID NO:7; and SEQ ID NO:10; or complements thereof;
 
(21) the nucleotide sequences as set forth in SEQ ID NO:1; SEQ ID NO:5; and SEQ ID NO:10; or complements thereof; or
 
(22) a nucleotide sequence that shares at least 75%, 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 97.5%, 98.0%, 98.5%, 99.0%, or 99.5% sequence identity with one nucleotide sequence of (1)-(21) or a complement thereof.
 
         [0084]    Such chimeric gene regulatory units are advantageous as it was surprisingly found that they exhibit higher recombinant protein production levels in CHO DG44 cells compared with wild type gene regulatory units or different chimeric gene regulatory units. 
         [0085]    Accordingly, in various embodiments, the isolated nucleic acid molecule of the invention comprising the functional chimeric gene regulatory unit and the at least one nucleotide sequence encoding for a molecule of interest has increased expression activity to express a molecule of interest in Chinese Hamster Ovary (CHO) DG44 cells compared to an isolated nucleic acid molecule comprising a naturally occurring gene regulatory unit and a nucleotide sequence encoding for the molecule of interest. In preferred embodiments, the increased expression activity of the functional chimeric gene regulatory unit is at least 1.1-fold, 1.2-fold, 1.3-fold, 1.4-fold, 1.5-fold, 1.6-fold or 1.7-fold higher compared to the naturally occurring gene regulatory unit. 
         [0086]    In various embodiments, the chimeric gene regulatory unit having increased expression activity in CHO DG44 cells comprises, consists essentially of or consists of (i) a nucleotide sequence as set forth in SEQ ID Nos. 34, 36, 37, 45, 47-52, 56, 57, 59-62, 64-67, 71 or a complement thereof; or (ii) a nucleotide sequence that shares at least 75%, 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 97.5%, 98.0%, 98.5%, 99.0%, or 99.5% sequence identity with a nucleotide sequence of (i), or a complement thereof. 
         [0087]    Such chimeric gene regulatory units are advantageous as it was surprisingly found that they exhibit higher recombinant protein production levels as achieved with wild type gene regulatory units or different chimeric gene regulatory units. 
         [0088]    In various embodiments, the chimeric gene regulatory unit comprises at least one binding site for a transcription factor. 
         [0089]    In preferred embodiments, the at least one binding site for a transcription factor is comprised in the enhancer, the core promoter or the intron. 
         [0090]    As used herein the term “transcription factor” refers to a protein that binds to specific DNA sequences, thereby controlling the rate of transcription of genetic information from DNA to messenger RNA (mRNA). Transcription factors perform this function alone or with other proteins in a complex, by promoting (as an activator), or blocking (as a repressor) the recruitment of RNA polymerase to specific genes. A defining feature of transcription factors is that they contain one or more DNA-binding domains (DBDs), which attach to specific sequences of DNA adjacent to the genes that they regulate. Herein, it is preferred that the recruited transcription factors activate RNA polymerase binding and function. 
         [0091]    In preferred embodiments, the transcription factor is specificity protein 1 (Sp1) transcription factor. This may be advantageous as it has been shown that the SP1 binding site may enhance expression during long term culture. The Sp1 transcription factor may comprise, consist essentially of or consist of the polypeptide sequence as set forth in SEQ ID NO:74 or SEQ ID NO:75, or may be a fragment thereof, with said fragment being functional in that it retains at least 50% activity of the full length sequence. Alternatively, in other preferred embodiments, the at least one binding site for a transcription factor contained in the nucleic acid molecules described herein comprises, consists essentially of or consists of the nucleotide sequence set forth in SEQ ID NO:76 (5′-(G/T)GGGCGG(G/A)(G/A)(C/T)-3′). 
         [0092]    The use of a transcription factor is advantageous as it represents an additional tool for controlling and improving the rate of transcription of genetic information from DNA to messenger RNA and hence achieving higher expression levels. 
         [0093]    In a further aspect, the invention relates to a vector comprising the isolated nucleic acid molecule of the invention. 
         [0094]    As used herein the term “vector” refers to a nucleic acid molecule used as a vehicle to artificially carry foreign genetic material into another cell, where it can be replicated and/or expressed. The four major types of vectors are plasmids, viral vectors, cosmids, and artificial chromosomes. Common to all engineered vectors are an origin of replication, a multicloning site, and a selectable marker. The vector itself is generally a nucleic acid sequence that consists of an insert (transgene) and a larger sequence that serves as the “backbone” of the vector. The purpose of a vector, which transfers genetic information to another cell, is typically to isolate, multiply, or express the insert in the target cell. In preferred embodiments, the vector is a plasmid. 
         [0095]    In a still further aspect, the invention relates to a host cell comprising the isolated nucleic acid molecule of the invention and/or the vector of the invention. 
         [0096]    The term “host cell” as used herein means an organism that harbors the nucleic acid molecules comprising the chimeric gene regulatory unit as described herein. They may be integrated into the genome of the host cell or exist in separate form in the cell. 
         [0097]    In various embodiments, said host cell is a eukaryotic cell. In preferred embodiments, said host cell is a mammalian cell. In even more preferred embodiments said host cell is a Chinese hamster ovary (CHO) cell. In more preferred embodiments, the host cell is a CHO K1 cell or a CHO DG44 cell. 
         [0098]    The nucleic acid molecules described herein can be used to facilitate or enhance the expression of a given molecule of interest in a cell. It is understood that in such embodiments, said isolated nucleic acid molecule also comprises a nucleotide sequence encoding the molecule of interest being operably linked to the chimeric gene regulatory unit of the isolated nucleic acid molecule. 
         [0099]    In such methods for the expression of molecules of interest, in particular polypeptides, the actual expression may be performed by by in vitro transcription and translation or, more preferably, recombinantly in a suitable host cell under conditions that allow production of the molecule of interest. 
         [0100]    The host cell may be a cell as described above. 
         [0101]    Conditions that allow production of the molecule of interest include the various parameters of cell culture, including selection of the medium and the cultivating conditions, such as temperature, time, etc. All of these factors are well-known to those skilled in the art and can be easily adapted by using routine techniques. 
         [0102]    It is understood that all embodiments disclosed herein in relation to the nucleic acids of the invention are similarly applicable to the vectors, host cells, uses and methods, described herein, and vice versa. 
         [0103]    The present invention is further illustrated by the following examples. However, it should be understood, that the invention is not limited to the exemplified embodiments. 
       Examples 
       [0104]    Five natural promoters occurring upstream of the human cytomegalovirus immediate early gene (hCMV), of the murine cytomegalovirus immediate early gene (mCMV), the simian virus 40 (SV40), the human elongation factor-1α gene (hEF-1α) and the chicken β-actin gene (cA) were dissected into enhancers (E), core promoters (CP) and introns (I) ( FIG. 1 ). These enhancers, core promoters, and introns from different sources were then recombined to generate fifty-seven new enhancer-core promoter and enhancer-core promoter-intron combinations, referred to as chimeric gene regulatory units or hybrid promoters. 
         [0105]    Table 1 shows the different elements used for generation of the chimeric gene regulatory units while Table 2 shows the tested combinations. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Naturally occurring enhancers, promoters, and introns 
               
             
          
           
               
                   
                   
                 SEQ 
                 Core 
                 SEQ 
                   
                 SEQ 
               
               
                   
                 Enhanc- 
                 ID 
                 Promot- 
                 ID 
                   
                 ID 
               
               
                 Origin 
                 er 
                 No. 
                 er 
                 No. 
                 Intron 
                 No. 
               
               
                   
               
             
          
           
               
                 Human CMV 
                 hCMVE 
                 1 
                 hCMVP 
                 4 
                 hCMV 
                 9 
               
               
                 (hCMV) 
                   
                   
                   
                   
                 IntronA 
               
               
                   
                   
                   
                   
                   
                 (vI) 
               
               
                 Murine CMV 
                 mCMVE 
                 2 
                 mCMVP 
                 5 
               
               
                 (mCMV) 
               
               
                 SV40 
                 SV40E 
                 3 
                 SV40P 
                 6 
               
               
                 Human EF gene 
                   
                   
                 hEFP 
                 7 
                 EF 
                 10 
               
               
                 (hEF) 
                   
                   
                   
                   
                 Intron 
               
               
                   
                   
                   
                   
                   
                 (fI) 
               
               
                 Chicken beta 
                   
                   
                 cAP 
                 8 
                 cA 
                 11 
               
               
                 actin (cA) 
                   
                   
                   
                   
                 Intron 
               
               
                   
                   
                   
                   
                   
                 (aI) 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Assessed gene regulatory units 
               
             
          
           
               
                   
                 Name 
                 Enhancer 
                 Core promoter 
                 Intron 
                 SEQ ID No 
               
               
                   
               
             
          
           
               
                 1 
                 WT hCMV 
                 HCMVE 
                 hCMVP 
                   
                 12 
               
               
                 2 
                 WT mCMV 
                 MCMVE 
                 mCMVP 
                   
                 13 
               
               
                 3 
                 WT SV40 
                 SV40E 
                 SV40P 
                   
                 14 
               
               
                 4 
                 WT hEF 
                   
                 hEFP 
                 fI 
                 15 
               
               
                 5 
                 WT cA 
                   
                 cAP 
                 aI 
                 16 
               
               
                 6 
                 hCmC 
                 hCMVE 
                 mCMVP 
                   
                 17 
               
               
                 7 
                 hCS 
                 hCMVE 
                 SV40P 
                   
                 18 
               
               
                 8 
                 hCE 
                 hCMVE 
                 hEFP 
                   
                 19 
               
               
                 9 
                 hCA 
                 hCMVE 
                 CAP 
                   
                 20 
               
               
                 10 
                 mChC 
                 mCMVE 
                 hCMVP 
                   
                 21 
               
               
                 11 
                 mCS 
                 mCMVE 
                 SV40P 
                   
                 22 
               
               
                 12 
                 mCE 
                 mCMVE 
                 hEFP 
                   
                 23 
               
               
                 13 
                 mCA 
                 mCMVE 
                 CAP 
                   
                 24 
               
               
                 14 
                 ShC 
                 SV40E 
                 hCMVP 
                   
                 25 
               
               
                 15 
                 SmC 
                 SV40E 
                 mCMVP 
                   
                 26 
               
               
                 16 
                 SE 
                 SV40E 
                 hEFP 
                   
                 27 
               
               
                 17 
                 SA 
                 SV40E 
                 CAP 
                   
                 28 
               
               
                 18 
                 WT 
                 hCMVE 
                 hCMVP 
                 vI 
                 29 
               
               
                   
                 hCMVvI 
               
               
                 19 
                 hCmCvI 
                 hCMVE 
                 mCMVP 
                 vI 
                 30 
               
               
                 20 
                 hCSvI 
                 hCMVE 
                 SV40P 
                 vI 
                 31 
               
               
                 21 
                 hCEvI 
                 hCMVE 
                 hEFP 
                 vI 
                 32 
               
               
                 22 
                 hCAvI 
                 hCMVE 
                 CAP 
                 vI 
                 33 
               
               
                 23 
                 mCMVvI 
                 mCMVE 
                 mCMVP 
                 vI 
                 34 
               
               
                 24 
                 mChCvI 
                 mCMVE 
                 hCMVP 
                 vI 
                 35 
               
               
                 25 
                 mCSvI 
                 mCMVE 
                 SV40P 
                 vI 
                 36 
               
               
                 26 
                 mCEvI 
                 mCMVE 
                 hEFP 
                 vI 
                 37 
               
               
                 27 
                 mCAvI 
                 mCMVE 
                 CAP 
                 vI 
                 38 
               
               
                 28 
                 SV40vI 
                 SV40E 
                 SV40P 
                 vI 
                 39 
               
               
                 29 
                 ShCvI 
                 SV40E 
                 hCMVP 
                 vI 
                 40 
               
               
                 30 
                 SmCvI 
                 SV40E 
                 mCMVP 
                 vI 
                 41 
               
               
                 31 
                 SEvI 
                 SV40E 
                 hEFP 
                 vI 
                 42 
               
               
                 32 
                 SAvI 
                 SV40E 
                 CAP 
                 vI 
                 43 
               
               
                 33 
                 hCMVfI 
                 hCMVE 
                 hCMVP 
                 fI 
                 44 
               
               
                 34 
                 hCmCfI 
                 hCMVE 
                 mCMVP 
                 fI 
                 45 
               
               
                 35 
                 hCSfI 
                 hCMVE 
                 SV40P 
                 fI 
                 46 
               
               
                 36 
                 hCEfI 
                 hCMVE 
                 hEFP 
                 fI 
                 47 
               
               
                 37 
                 hCAfI 
                 hCMVE 
                 CAP 
                 fI 
                 48 
               
               
                 38 
                 mCMVfI 
                 mCMVE 
                 mCMVP 
                 fI 
                 49 
               
               
                 39 
                 mChCfI 
                 mCMVE 
                 hCMVP 
                 fI 
                 50 
               
               
                 40 
                 mCSfI 
                 mCMVE 
                 SV40P 
                 fI 
                 51 
               
               
                 41 
                 mCEfI 
                 mCMVE 
                 hEFP 
                 fI 
                 52 
               
               
                 42 
                 mCAfI 
                 mCMVE 
                 CAP 
                 fI 
                 53 
               
               
                 43 
                 SV40fI 
                 SV40E 
                 SV40P 
                 fI 
                 54 
               
               
                 44 
                 ShCfI 
                 SV40E 
                 hCMVP 
                 fI 
                 55 
               
               
                 45 
                 SmCfI 
                 SV40E 
                 mCMVP 
                 fI 
                 56 
               
               
                 46 
                 SEfI 
                 SV40E 
                 hEFP 
                 fI 
                 57 
               
               
                 47 
                 SAfI 
                 SV40E 
                 CAP 
                 fI 
                 58 
               
               
                 48 
                 hCMVaI 
                 hCMVE 
                 hCMVP 
                 aI 
                 59 
               
               
                 49 
                 hCmCaI 
                 hCMVE 
                 mCMVP 
                 aI 
                 60 
               
               
                 50 
                 hCSaI 
                 hCMVE 
                 SV40P 
                 aI 
                 61 
               
               
                 51 
                 hCEaI 
                 hCMVE 
                 hEFP 
                 aI 
                 62 
               
               
                 52 
                 hCAaI 
                 hCMVE 
                 CAP 
                 aI 
                 63 
               
               
                 53 
                 mCMVaI 
                 mCMVE 
                 mCMVP 
                 aI 
                 64 
               
               
                 54 
                 mChCaI 
                 mCMVE 
                 hCMVP 
                 aI 
                 65 
               
               
                 55 
                 mCSaI 
                 mCMVE 
                 SV40P 
                 aI 
                 66 
               
               
                 56 
                 mCEaI 
                 mCMVE 
                 hEFP 
                 aI 
                 67 
               
               
                 57 
                 mCAaI 
                 mCMVE 
                 CAP 
                 aI 
                 68 
               
               
                 58 
                 SV40aI 
                 SV40E 
                 SV40P 
                 aI 
                 69 
               
               
                 59 
                 ShCaI 
                 SV40E 
                 hCMVP 
                 aI 
                 70 
               
               
                 60 
                 SmCaI 
                 SV40E 
                 mCMVP 
                 aI 
                 71 
               
               
                 61 
                 SEaI 
                 SV40E 
                 hEFP 
                 aI 
                 72 
               
               
                 62 
                 SAaI 
                 SV40E 
                 CAP 
                 aI 
                 73 
               
               
                   
               
             
          
         
       
     
         [0106]    The different chimeric gene regulatory units were then inserted into antibody expression vectors for comparison of chimeric promoters in CHO K1 and CHO DG44 cells with the arrangement of the different elements in the vectors schematically shown in  FIG. 2 . 
         [0107]    Stably transfected CHO K1 pools were generated by transfecting 1×10 7  CHO K1 cells with 5 μg of an appropriate linearized mAb expressing plasmid containing a specific chimeric promoter and zeocin selection marker gene ( FIG. 2A ). Transfections were carried out using Nucleofactor kit V (Lonza, VCA1003) and program U-24 on a Nucleofector II system (Lonza, Cologne, Germany) following the manufacturer&#39;s instructions. The transfected cells were then resuspended in 2 mL protein free medium in 6-well suspension culture plate. At 24 h post-transfection, the transfected cell culture were centrifuged at ˜100×g for 5 min. Cell pellets were then resuspended in 25 mL protein free medium containing 600 μg/mL zeocin in 125 mL shake flasks to select for stable transfectants. The stably transfected pools were deemed successfully generated when viability of stably transfected pools recovered above 95%. Productivity of each stably transfected pool was determined in 125 mL shake flask batch cultures. Cells were seeded at 2×10 5  cells/mL. Cell density and viability were monitored using Vi-Cell every day until viability dropped to below 50%. The supernatant was collected at the end of culture and analyzed for mAb concentration using a nephelometric method on an IMMAGE 800 immunochemistry system (Beckman Coulter, Buckinghamshire, England). The IMMAGE 800 system uses anti-human Fc region antibodies for IgG detection. The average titer of duplicated pools generated using each promoter was shown in  FIG. 3A . 
         [0108]    Transfection of CHO DG44 cells were carried out using the same protocol as for CHO K1 cells. The transfected cells were then resuspended in 2 mL protein free medium containing hypoxanthine and thymine (HT) in 6-well suspension culture plate. At 24 h post-transfection, the transfected cell culture were centrifuged at ˜100×g for 5 min. Cell pellets were then resuspended in 25 mL protein free medium without HT in 125 mL shake flasks to select for stable transfectants. When viability of stably transfected pools recovered above 95%, stepwise methotrexate (MTX, Sigma, M8407) amplification was carried out with concentrations of 50 nM to 500 nM. Productivity of amplified pools at 500 nM was determined using the same protocol as for stably transfected CHO K1 cells. The average titer of duplicated pools generated using each promoter was shown in  FIG. 3   b.