Patent Publication Number: US-2022235339-A1

Title: FCE mRNA Capping Enzyme Compositions, Methods and Kits

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 17/246,454 filed Apr. 30, 2021, which is a divisional of U.S. application Ser. No. 17/160,256 filed Jan. 27, 2021, which issued as U.S. Pat. No. 11,028,379 on Jun. 8, 2021. The contents of all of the above are hereby incorporated in their entirety by reference. 
    
    
     SEQUENCE LISTING STATEMENT 
     This disclosure includes a Sequence Listing submitted electronically in ascii format under the file name “NEB-438-US_ST25.txt”. This Sequence Listing is incorporated herein in its entirety by this reference. 
     BACKGROUND 
     The potential for mRNA vaccines to transform the treatment of infectious diseases has gained considerable traction since it was first proposed. In addition, mRNA as a therapeutic modality may supplement functional therapeutic proteins that are not antigens, for example, erythropoietin, CFTR, or genome editing proteins (e.g., CRISPR-Cas9, meganucleases). Manufacturing mRNA may be cell-free and scalable. Once the sequence of a desired antigen is provided, the time required to produce clinical batches of vaccine might be weeks instead of months. Such rapid production may limit or even avert widespread outbreaks. In addition, mRNA alternatives to a number of protein replacement regimens are envisioned. Production of stable mRNA capable of efficient translation upon introduction to a subject may require an appropriate cap structure, such as a Cap 0 structure (m7Gppp5′N) at the 5′ end. Capping by a capping enzyme may be desired or even required for production of an effective RNA vaccine. For example, a suitable cap structure may impact the stability and translatability of an RNA vaccine. 
     SUMMARY 
     Accordingly, needs have arisen for improved compositions, kits, and methods of making RNA vaccines having an appropriate cap structure. The present disclosure relates to systems, apparatus, compositions, and/or methods including non-naturally occurring single-chain RNA capping enzymes. In some embodiments, an RNA capping enzyme may include an FCE variant having (a) an amino acid sequence at least 90% identical to positions 1 to 878 of SEQ ID NO: 1, and/or (b) a substitution relative to SEQ ID NO: 1 at a position selected from positions corresponding to positions 215, 337, 572, 648, and 833 (e.g., a position selected from positions corresponding to position 215, 337, and 572) of SEQ ID NO: 1. An FCE variant, in some embodiments, may comprise a second substitution at a position (i) other than the position of the first substitution and (ii) corresponding to position 215, 337, 572, 648, or 833 of SEQ ID NO: 1. An FCE variant, in some embodiments, may comprise a third substitution at a position (iii) other than the position of the first and second substitutions and (iv) corresponding to position 215, 337, 572, 648, or 833 of SEQ ID NO: 1. An FCE variant, in some embodiments, may comprise a fourth substitution at a position (v) other than the position of the first, second and third substitutions and (vi) corresponding to position 215, 337, 572, 648, or 833 of SEQ ID NO: 1. In some embodiments, an FCE variant may have an amino acid sequence that is at least 90% identical, but not 100% identical to SEQ ID NO: 1. In some embodiments, an FCE variant may have an amino acid sequence that is at least 90% identical, but not 100% identical to SEQ ID NO: 1. An FCE variant (a) may have an amino acid sequence (a) at least 90% identical to SEQ ID NO: 26, and/or (b) may have an amino acid other than asparagine at a position selected from positions corresponding to positions X215, X337, X572, X648, and X833 of SEQ ID NO: 26. 
     In some embodiments, an FCE variant may include additional peptides (e.g., for sorting, processing, and/or purification of the catalytically active portion of the molecule). For example, an FCE variant may comprise a purification tag and/or a sorting signal. In some embodiments, an FCE variant may comprise, in an N-terminal to C-terminal direction, (a) a purification tag or sorting signal peptide, and (b)(i) an amino acid sequence at least 90% identical to positions 1 to 878 of SEQ ID NO: 1, and/or (ii) a substitution relative to SEQ ID NO: 1 at a position selected from positions corresponding to positions 215, 337, 572, 648, and 833. In some embodiments, an FCE variant may further comprise an insertion (e.g., a sorting signal or a purification tag) on the N-terminal side of the position corresponding to position 1 of SEQ ID NO: 1. In some embodiments, an FCE variant may further comprise an insertion (e.g., a sorting signal or a purification tag) on the C-terminal side of the position corresponding to position 878 of SEQ ID NO: 1. 
     Compositions, according to some embodiments, may include an FCE variant (e.g., any of the foregoing FCE variants) and a polynucleotide, wherein the polynucleotide comprises ribonucleotides and deoxyribonucleotides. A composition, according to some embodiments, may comprise an FCE variant (e.g., any of the foregoing FCE variants) and a polyribonucleotide. A composition may optionally comprise, for example, a cap, an NTP, a modified NTP, a buffer, S-adenosylmethionine, and/or an RNase inhibitor, according to some embodiments. 
     The present disclosure relates, in some embodiments, to FCE variant transcripts. For example, an FCE variant transcript may comprise a transcript (e.g., polynucleotide transcript comprising RNA) encoding an amino acid sequence having (a) at least 90% identical to positions 1 to 878 of SEQ ID NO: 1, and (b) a substitution relative to SEQ ID NO: 1 at a position selected from positions corresponding to positions 215, 337, 572, 648, and 833 (e.g., a position selected from positions corresponding to position 215, 337, and 572) of SEQ ID NO: 1, and (c) optionally, a cap. An amino acid sequence encoded by an FCE variant transcript, in some embodiments, may comprise a second substitution at a position (i) other than the position of the first substitution and (ii) corresponding to position 215, 337, 572, 648, or 833 of SEQ ID NO: 1. An amino acid sequence encoded by an FCE variant transcript, in some embodiments, may comprise a third substitution at a position (iii) other than the position of the first and second substitutions and (iv) corresponding to position 215, 337, 572, 648, or 833 of SEQ ID NO: 1. An amino acid sequence encoded by an FCE variant transcript, in some embodiments, may comprise a fourth substitution at a position (v) other than the position of the first, second and third substitutions and (vi) corresponding to position 215, 337, 572, 648, or 833 of SEQ ID NO: 1. 
     An FCE variant transcript, according to some embodiments, may comprise in a 5′ to 3′ direction, (I) a nucleotide sequence encoding a purification tag or a sorting signal peptide, and (II) an FCE variant transcript comprising, for example, a transcript encoding an amino acid sequence having (A) at least 90% identical to positions 1 to 878 of SEQ ID NO: 1, and (B) a substitution relative to SEQ ID NO: 1 at a position selected from positions corresponding to positions 215, 337, 572, 648, and 833 of SEQ ID NO: 1, and (C) optionally, a cap, wherein the purification tag or sorting signal peptide is operably linked to the FCE variant encoded by (II). 
     In some embodiments, an FCE variant transcript may comprise in a 5′ to 3′ direction, (I) an FCE variant transcript comprising, for example, a transcript encoding an amino acid sequence having (A) at least 90% identical to positions 1 to 878 of SEQ ID NO: 1, and (B) a substitution relative to SEQ ID NO: 1 at a position selected from positions corresponding to positions 215, 337, 572, 648, and 833 of SEQ ID NO: 1, and (C) optionally, a cap, and (II) a nucleotide sequence encoding a purification tag or a sorting signal peptide, wherein the purification tag or sorting signal peptide is operably linked to the FCE variant encoded by (I). In some embodiments, an FCE variant transcript may encode an amino acid sequence further comprising an insertion (e.g., a sorting signal or a purification tag) on the N-terminal side of the position corresponding to position 1 of SEQ ID NO: 1 and/or on the C-terminal side of the position corresponding to position 878 of SEQ ID NO: 1. In some embodiments, an FCE variant transcript comprises (C) a cap (e.g., a natural cap, a dinucleotide cap, or a modified cap). 
     The present disclosure further relates to cells and cell-based and cell-free methods of producing FCE variants and FCE variant transcripts. For example, a cell may comprise one or more FCE variants and or one or more FCE variant transcripts. In some embodiments, a cell may comprise an FCE variant transcript may comprise a polynucleotide (e.g., polynucleotide transcript comprising RNA) encoding an amino acid sequence having (a) at least 90% identical to positions 1 to 878 of SEQ ID NO: 1, and (b) a substitution relative to SEQ ID NO: 1 at a position selected from positions corresponding to positions 215, 337, 572, 648, and 833 (e.g., a position selected from positions corresponding to position 215, 337, and 572) of SEQ ID NO: 1, and (c) optionally, a cap. A cell may comprise a genomic or an extra-genomic polynucleotide (e.g., a DNA expression vector or cassette) having a sequence encoding an FCE variant having (a) an amino acid sequence at least 90% identical to positions 1 to 878 of SEQ ID NO: 1, and/or (b) a substitution relative to SEQ ID NO: 1 at a position selected from positions corresponding to positions 215, 337, 572, 648, and 833 (e.g., a position selected from positions corresponding to position 215, 337, and 572) of SEQ ID NO: 1. A cell, in some embodiments, may be a eukaryotic cell, for example, a yeast cell. 
     The present disclosure further relates to methods of capping a target RNA. A capping method may comprise, for example, contacting (a) an FCE variant having (i) an amino acid sequence at least 90% identical to positions 1 to 878 of SEQ ID NO: 1, and (ii) a substitution at a position selected from positions corresponding to positions 215, 337, 572, 648, and 833 of SEQ ID NO: 1, (b) a target RNA (e.g., an uncapped RNA), and (c) one or more of a cap, an NTP, and a modified NTP, and optionally (d) a buffer, S-adenosylmethionine, and/or an RNase inhibitor, to form a capped target RNA. In some embodiments, contacting may comprise contacting at a temperature in the range of 37° C.-60° C. and/or for a time in the range of seconds to hours (e.g., 60 seconds to 16 hours). A target RNA may or may not be capped (e.g., before contacting). According to some embodiments, a method may comprise contacting a target RNA (e.g., a capped target RNA) with a decapping enzyme to form an uncapped target RNA, for example, prior to contacting the target RNA with the FCE variant. A method may further comprise contacting the capped target RNA with one or more pharmaceutically acceptable additives. 
     A method of producing an FCE variant may comprise, for example, contacting (a) an FCE variant transcript comprising an RNA encoding an amino acid sequence having (i) an amino acid sequence at least 90% identical to positions 1 to 878 of SEQ ID NO: 1, and (ii) a substitution at a position selected from positions corresponding to positions 215, 337, 572, 648, and 833 of SEQ ID NO: 1 with (b) an expression system (e.g., a cell-based or cell-free expression system). 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The file of this patent contains at least one drawing executed in color. Copies of this patent with color drawing(s) will be provided by the Patent and Trademark Office upon request and payment of the necessary fee. 
         FIGS. 1A and 1B  show general maps of yeast expression vectors.  FIG. 1A  shows a general map of pD912 (ATUM, formerly DNA 2.0) and  FIG. 1B  shows a general map of pKLMF-EK (New England Biolabs) used to assemble plasmids containing FCE, α-mating factor and MBP-fusion constructs respectively. 
         FIG. 2  shows schematically the linear integrative expression cassettes that were prepared by SacI-HF restriction digestion or PCR from the assembled plasmids as a DNA template. The assembled plasmids and linear cassettes have the following design: GAP or LAC4 promoter, followed by the α-mating factor pre-pro domain (secretion) or malE gene (cytoplasmic), FCE with carboxy-terminal His-tag; AOX1 terminator sequence (T AOX1 ) or  K. lactis  LAC4 transcription terminator (TT); zeocin resistance gene under control of the ILV5 promoter (P ILV5 +Zeo r ) or a fungal acetamidase selectable marker gene (amdS) expressed from the yeast ADH1 promoter (P ADH1 ); the sequence of an  E. coli  origin of replication (Ori_pUC); flanking sequences for the targeted integration (3′ Promoter fragment contains the sequence of the actual promoter). pKLMF-EK also contains an ampicillin resistance gene (Ap R ) for selection in  E. coli.    
         FIGS. 3A and 3B  show effective expression of FCE constructs in  Pichia pastoris  and  Kluyveromyces lactis .  FIG. 3A  shows secreted expression of FCE wild type (WT) and individual FCE N-glycan variants in  P. pastoris  cells transformed with constructs containing GAP promoter. Transformants were grown in Buffered Minimal Glycerol medium, BMGY with 1% glycerol at 30° C. for 48 hours. The spent culture medium was harvested, concentrated and buffer exchanged. After overnight digestion with Endo Hf, the spent media was analyzed by SDS-PAGE on a 4-20% polyacrylamide gel followed by western blotting with a His-tag antibody. Lanes 1,2: FCE-WT −/+Endo Hf, respectively; Lanes 3,4: FCE-N215Q −/+Endo Hf, respectively; Lanes 5,6: FCE-N337Q −/+Endo Hf, respectively; Lanes 7,8: FCE-N572Q −/+Endo Hf, respectively; Lanes 9,10:  P. pastoris  (empty strain) −/+Endo Hf, respectively.  FIG. 3B  shows cytoplasmic expression of MBP-FCE in  K. lactis  cells transformed with a construct containing the  K. lactis  LAC4 promoter. The transformants were grown in yeast extract peptone (YEP) medium with 2% galactose at 30° C. for 48 hours. Cells were harvested, and cell lysates were prepared by sonication and analyzed by SDS-PAGE on a 4-20% polyacrylamide gel, followed by western blotting with a His-tag antibody. Lanes 1,2—cell lysates of  K. lactis  transformants #1 and #2 expressing MBP-FCE; lane 3—control  K. lactis  cell lysate. 
         FIG. 4A and 4B  shows the activity of expressed FCE proteins.  FIG. 4A  shows spent culture media from  P. pastoris  cells treated with Endo Hf.  FIG. 4B  shows cell lysates from  K. lactis  cells. The activity was assayed using an in vitro mRNA capping assay as described in Examples section V. 
         FIG. 5  shows secreted expression of FCE WT, FCE (N215Q/N337Q/N572Q) and FCE (N215Q/N337Q/N572Q/N648Q/N833Q) mutants in  Pichia pastoris  cells transformed with constructs containing the GAP promoter. Transformants were grown in Buffered Minimal Glycerol medium, BMGY with 1% glycerol at 30° C. for 48 hours. Spent culture media were harvested, concentrated, buffer exchanged and purified using NEBExpress Ni Spin Columns The load (spent culture media) and elution fractions were analyzed by SDS-PAGE on a 4-20% polyacrylamide gel and stained using Simply Blue Safe Stain (Thermofisher). Lanes 1,2: spent culture medium and elution fraction of FCE-WT; Lanes 3,4: spent culture medium and elution fraction of FCE (N215Q/N337Q/ N572Q) mutant; Lanes 5,6: spent culture medium and elution fraction of FCE (N215Q/337Q/N572Q/N648Q/N833Q) mutant; Lanes 7,8: spent culture medium and elution fraction of control  P. pastoris  MutS (empty strain); M: Color Prestained Protein Standard, Broad Range (NEB). 
         FIG. 6  shows the activity of the concentrated and buffer exchanged spent culture media, from  P. pastoris  cells, of FCE WT, FCE (N215Q/N337Q/N572Q), FCE (N215Q/N337Q/N572Q/N648Q/N833Q) and control  P. pastoris  MutS (empty strain). 
         FIG. 7A  and  FIG. 7B  represent the secreted expression of FCE wild type (WT), (N215Q/N337Q/N572Q) and (N215Q/N337Q/N572Q/N648Q/N833Q) N-glycan mutants in  Pichia pastoris  cells transformed with constructs containing GAP promoter and control  P. pastoris  MutS (empty strain). The transformants were grown in Buffered Minimal Glycerol medium, BMGY with 1% glycerol at 30° C. for 48 hours. The spent culture medium was harvested, concentrated and buffer exchanged. After overnight digestion with Endo Hf, the spent medium was analyzed by SDS-PAGE on a 4-20% polyacrylamide gel followed by western blotting with a His-tag antibody. Lanes 1,2: FCE-WT −/+Endo Hf; Lanes 3,4: FCE (N215Q/N337Q/N572Q) −/+Endo Hf; Lanes 5,6: FCE (N215Q/N337Q/572Q/N648Q/N833Q) −/+Endo Hf; Lanes 7,8: control  P. pastoris  (empty strain) −/+Endo Hf; M: Color Prestained Protein Standard, Broad Range (NEB).  FIG. 7A  is a Simply Blue Safe Stained gel.  FIG. 7B  is a corresponding Western blot. 
     
    
    
     BRIEF DESCRIPTION OF THE SEQUENCES 
     Sequences of example polynucleotides and polypeptides, according to some embodiments, are elaborated in the SEQUENCE LISTING, in which: 
     SEQ ID NO: 1 illustrates an amino acid sequence of an FCE variant having a C-terminal 8×His tag (879-886) in which positions 215, 337, 572, 648, and/or 833 may be glycosylated or replaced with any other amino acid (e.g., glutamine); 
     SEQ ID NO: 2 illustrates an amino acid sequence of an FCE variant having a region with a maltose binding protein (MBP), Linker, and enterokinase (EK) cleavage sequence (DDDK) (1-388) and a C-terminal 8×His tag (1267-1274); 
     SEQ ID NO: 3 illustrates a forward primer for amplification of an FCE variant in which positions 1-20 overlap with the signal peptide sequence in the pD912 vector (SEQ ID NO: 24 or 26); 
     SEQ ID NO: 4 illustrates a reverse primer for amplification of an FCE variant in which positions 1-20 overlap with the T AOX1  sequence in the pD912 vector (SEQ ID NO: 24 or 26); 
     SEQ ID NO: 5 illustrates a forward primer for amplification of a pD912 vector fragment; 
     SEQ ID NO: 6 illustrates a reverse primer for amplification of a pD912 vector fragment; 
     SEQ ID NO: 7 illustrates a forward primer adapted (e.g., at positions 11-13) for modifying the codon corresponding to position 215 of SEQ ID NO: 1 from asparagine to glutamine; 
     SEQ ID NO: 8 illustrates a reverse primer adapted for modifying the codon corresponding to position 215 of SEQ ID NO: 1 from asparagine to glutamine; 
     SEQ ID NO: 9 illustrates a forward primer adapted (e.g., at positions 11-13) for modifying the codon corresponding to position 337 of SEQ ID NO: 1 from asparagine to glutamine; 
     SEQ ID NO: 10 illustrates a reverse primer adapted for modifying the codon corresponding to position 337 of SEQ ID NO: 1 from asparagine to glutamine; 
     SEQ ID NO: 11 illustrates a forward primer adapted (e.g., at positions 11-13) for modifying the codon corresponding to position 572 of SEQ ID NO: 1 from asparagine to glutamine; 
     SEQ ID NO: 12 illustrates a reverse primer adapted for modifying the codon corresponding to position 572 of SEQ ID NO: 1 from asparagine to glutamine; 
     SEQ ID NO: 13 illustrates a forward primer adapted (e.g., at positions 11-13) for modifying the codon corresponding to position 648 of SEQ ID NO: 1 from asparagine to glutamine; 
     SEQ ID NO: 14 illustrates a reverse primer adapted for modifying the codon corresponding to position 648 of SEQ ID NO: 1 from asparagine to glutamine; 
     SEQ ID NO: 15 illustrates a forward primer adapted (e.g., at positions 11-13) for modifying the codon corresponding to position 833 of SEQ ID NO: 1 from asparagine to glutamine; 
     SEQ ID NO: 16 illustrates a reverse primer adapted for modifying the codon corresponding to position 833 of SEQ ID NO: 1 from asparagine to glutamine; 
     SEQ ID NO: 17 illustrates a forward primer for amplification of an FCE variant in which positions 1-20 overlap with the malE sequence in the pKLMF-EK vector; 
     SEQ ID NO: 18 illustrates a reverse primer for amplification of an FCE variant in which positions 1-20 overlap with multiple cloning site sequence in the pKLMF-EK vector; 
     SEQ ID NO: 19 illustrates a forward primer for amplification of a pKLMF-EK vector fragment; 
     SEQ ID NO: 20 illustrates a reverse primer for amplification of a pKLMF-EK vector fragment; 
     SEQ ID NO: 21 illustrates a forward primer for amplification of an assembled linear expression cassette of pKLMF-EK-FCE; 
     SEQ ID NO: 22 illustrates a reverse primer for amplification of an assembled linear expression cassette of pKLMF-EK-FCE; 
     SEQ ID NO: 23 illustrates a substrate RNA for in vitro capping reactions; 
     SEQ ID NO: 24 illustrates a nucleotide sequence of an expression plasmid, namely pD912-FCE(N215Q/N337Q/N572Q) expression plasmid; 
     SEQ ID NO: 25 illustrates a fully processed mature FCE variant protein with asparagine to glutamine substitutions at positions corresponding to positions 215, 337, and 572 of SEQ ID NO: 1; 
     SEQ ID NO: 26 illustrates a nucleotide sequence of an expression plasmid, namely pD912-FCE (N215Q/N337Q/N572Q N648Q/N833Q) expression plasmid; 
     SEQ ID NO: 27 illustrates a fully processed mature FCE variant protein with asparagine to glutamine substitutions at positions corresponding to positions 215, 337, 572, 648, AND 833 of SEQ ID NO: 1; and 
     SEQ ID NO: 28 illustrates an amino acid sequence of an FCE variant in which positions 215, 337, 572, 648 and/or 833 may comprise any amino acid (e.g., optionally, any amino acid other than asparagine. 
     DETAILED DESCRIPTION 
     Aspects of the present disclosure can be further understood in light of the embodiments, section headings, figures, descriptions and examples, none of which should be construed as limiting the entire scope of the present disclosure in any way. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the disclosure. 
     Each of the individual embodiments described and illustrated herein has discrete components and features which can be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present teachings. Any recited method can be carried out in the order of events recited or in any other order which is logically possible. 
     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 to which this disclosure belongs. Still, certain terms are defined herein with respect to embodiments of the disclosure and for the sake of clarity and ease of reference. 
     Sources of commonly understood terms and symbols may include: standard treatises and texts such as Kornberg and Baker, DNA Replication, Second Edition (W. H. Freeman, New York, 1992); Lehninger, Biochemistry, Second Edition (Worth Publishers, New York, 1975); Strachan and Read, Human Molecular Genetics, Second Edition (Wiley-Liss, New York, 1999); Eckstein, editor, Oligonucleotides and Analogs: A Practical Approach (Oxford University Press, New York, 1991); Gait, editor, Oligonucleotide Synthesis: A Practical Approach (IRL Press, Oxford, 1984); Singleton, et al., Dictionary of Microbiology and Molecular biology, 2d ed., John Wiley and Sons, New York (1994), and Hale &amp; Markham, the Harper Collins Dictionary of Biology, Harper Perennial, N.Y. (1991) and the like. 
     In the context of the present disclosure, the singular forms “a” and “an” include plural referents unless the context clearly dictates otherwise. For example, the term “a protein” refers to one or more proteins, i.e., a single protein and multiple proteins. It is further noted that the claims can be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only” and the like in connection with the recitation of claim elements or use of a “negative” limitation. 
     Numeric ranges are inclusive of the numbers defining the range. All numbers should be understood to encompass the midpoint of the integer above and below the integer i.e., the number 2 encompasses 1.5-2.5. The number 2.5 encompasses 2.45-2.55 etc. When sample numerical values are provided, each alone may represent an intermediate value in a range of values and together may represent the extremes of a range unless specified. 
     In the context of the present disclosure, “active” with reference to an enzyme refers to detectable catalytic activity by any available assay including those set forth in the Examples. For example, an active FCE capping enzyme has at least detectable RNA-triphosphatase activity, at least detectable RNA guanylyltransferase activity, or at least detectable RNA N7-guanine methyltransferase activity. 
     Each catalytic activity may be tested separately and/or in combination. Techniques for detecting TPase activity include, for example, combining the subject enzyme with γ- 32 P-poly(A) RNA, separating reaction products using thin layer chromatography, excising Pi spots and subjecting to scintillation counting to measure Pi (and indirectly pp-poly(A) RNA) release from ppp-poly(A) RNA. Techniques for detecting GTase activity include an enzyme-GMP intermediate assay in which, for example, the subject enzyme is combined with α- 32 P-GTP, reaction products are separated by SDS-PAGE, and the enzyme-GMP covalent intermediate formed (if any) is detected (e.g., by autoradiography). This activity can also be assessed in a cap formation reaction in which, for example, the subject enzyme is combined with α- 32 P-GTP and poly(A) RNA and the reaction products are analyzed by TCA precipitation, filter binding, and scintillation counting (measuring the amount of Gppp-poly(A) RNA). Techniques for detecting MTase activity include combining a radiolabeled capped poly(A) RNA (e.g., α- 32 P-GTP with poly(A) RNA) and VCE to produce G*ppp-poly(A) RNA, contacting that product with SAM and the subject enzyme, digesting with P1 nuclease, separating reaction products by thin layer chromatography, and analyzing excised spots by scintillation counting to measure the amount of m7GpppA from poly(A) RNA (JBC (1989) 264:9690-9695). MTase activity may also be detected by combining the subject enzyme with GpppA (New England Biolabs, Inc.) and  3 H—S-adenosyl methionine, separating reaction products by thin layer chromatography, and analyzing excised bands by scintillation counting to measure amount of m7GpppA formed (RNA (2008) 14: 2297-2304). 
     In the context of the present disclosure, “buffer” and “buffering agent” refer to a chemical entity or composition that itself resists and, when present in a solution, allows such solution to resist changes in pH when such solution is contacted with a chemical entity or composition having a higher or lower pH (e.g., an acid or alkali). Examples of suitable non-naturally occurring buffering agents that may be used in disclosed compositions, kits, and methods include, for example, Tris, HEPES, TAPS, MOPS, tricine, or MES. 
     In the context of the present disclosure, “cap” refers to a natural cap, such as  7 mG, and to a compound of the general formula R3p 3 N1-[p-N](x), where R3 is a guanine, adenine, cytosine, uridine or analogs thereof (e.g., N 7 -methylguanosine; m 7 G), p 3  is a triphosphate linkage, N1 and Nx are ribonucleosides, x is 0-8 and p is, independently for each position, a phosphate group, a phosphorothioate, a phosphorodithioate, an alkylphosphonate, an arylphosphonate, or a N-phosphoramidate linkage. R3 may have an added label at the 2′ or 3′ position of the ribose, and, in some embodiments, the label may be an oligonucleotide, a detectable label such as a fluorophore, or a capture moiety such as biotin or desthiobiotin, where the label may be optionally linked to the ribose of the nucleotide by a linker, for example. See, e.g., WO 2015/085142. A cap may have a cap 0 structure, a cap 1 structure or a cap 2 structure (e.g., as reviewed in Ramanathan, Nucleic Acids Res. 2016 44: 7511-7526), depending on which enzymes and/or whether SAM is present in the capping reaction. 
     Caps include dinucleotide cap analogs, e.g., of formula m 7 G(5′)p3(5′)G, in which a guanine nucleotide (G) is linked via its 5′OH to the triphosphate bridge. In some dinucleotide caps the 3′-OH group is replaced with hydrogen or OCH 3  (U.S. Pat. No. 7,074,596; Kore, Nucleosides, Nucleotides, and Nucleic Acids, 2006, 25: 15 307-14; and Kore, Nucleosides, Nucleotides, and Nucleic Acids, 2006, 25: 337-40). Dinucleotide caps include m 7 G(5′)p 3 G, 3′-OMe-m 7 G(5′)p 3 G (ARCA). Caps also include trinucleotide cap analogs (defined below) as well as other, longer, molecules (e.g., cap that have four, five or six or more nucleotides joined to the triphosphate bridge). In a cap analog, the 2′ and 3′ groups on the ribose of the m 7 G may be independently selected O-alkyl (e.g., O-methyl), halogen, a linker, hydrogen or a hydroxyl and the sugars 20 in N1 and NX may be independently selected from ribose, deoxyribose, 2′-O-alkyl, 2′-O-methoxyethyl, 2′-O-allyl, 2′-O-alkylamine, 2′-fluororibose, and 2′-deoxyribose. N1 and NX may independently (for each position) comprise a base selected from adenine, uridine, guanine, or cytidine or analogs of adenine, uridine, guanine, or cytidine, and nucleotide modifications can be selected from N 6 -methyladenine, N 1 -methyladenine,N 6 -2′ -Odimethyladenosine, pseudouridine, N 1 -methylpseudouridine, 5-iodouridine, 4-thiouridine, 2-thiouridine, 5-methyluridine, pseudoisocytosine, 5-methoxycytosine, 2-thiocytosine, 5-hydroxycytosine, N 4 -methylcytosine, 5-hydroxymethylcytosine, hypoxanthine, N1-methylguanine, O 6 -methylguanine, 1-methyl-guanosine, N 2 -methylguanosine, N 2 ,N 2 -dimethyl-guanosine, 2-methyl-O-2′-O-methyl-guanosine, N 2 ,N 2 -dimethyl-2′-O-methyl-guanosine, 1-methyl-2′-O-methyl-guanosine, N 2 ,N 7 -dimethyl-2′-O-methyl-guanosine, and isoguanineadenine. 
     In the context of the present disclosure, “capping” refers to the addition of a cap onto the 5′ end of an RNA. Caps may be added at the 5′ end of an RNA (e.g., an uncapped RNA transcript) chemically or enzymatically apart from transcription or co-transcriptionally to yield a 5′ capped RNA. Capping may or may not be reversible. 
     In the context of the present disclosure, “decapping enzyme” refers to an enzyme that removes a cap from an RNA, leaving the RNA with a 5′ monophosphate, but otherwise unchanged. Decapping enzymes may have pyrophosphohydrolase activity. Examples of decapping enzymes include enzymes in the Nudix hydrolase family (e.g., RppH, DCP1/DCP2 complex, NUDT16, African swine fever virus decapping enzyme), DXO family (e.g., Dxo1p, Railp), histidine triad family (e.g., DCPS, Fhit), and Apa-H-like phosphatase. Examples of decapping enzymes are described in Kramer and McLennan, 2019, WIREs RNA 10(1)e1511. 
     In the context of the present disclosure, “expression system” refers to systems for producing a protein from a polynucleotide template comprising components to produce the protein according to an RNA template (e.g., enzymes, amino acids, an energy source), (optionally) components to produce the RNA template according to another RNA template or a DNA template (e.g., enzymes, nucleotides, an energy source). An expression system may comprise a bacterial (e.g.,  Escherichia coli ) or yeast (e.g.,  Kluyveromyces lactis  or  Pichia pastoris ) expression system in which the protein is encoded by an RNA or DNA template within an expression cassette, a plasmid or other expression vector. An expression system may comprise a viral expression system in which the protein is encoded by an RNA or DNA template (e.g., in an expression cassette) within a viral genome or viral expression vector. Examples of cell-free expression systems may include or comprise cell extracts of  Escherichia coli  S30, rabbit reticulocytes or wheat germ, PUREEXPRESS® (New England Biolabs, Ipswich, Mass.), an insect cell extract system (e.g., Promega # L1101), or HeLa cell lysate-based protein expression systems (e.g., Thermo Fisher Scientific # 88882). An expression cassette may comprise, in some embodiments, an expression control sequence (e.g., promoter), a coding sequence encoding the gene product (e.g., protein) of interest (e.g., a vaccinia capping enzyme fusion), and/or one or more termination sequences (e.g., terminators). An expression control sequence (e.g., promoter) may comprise any promoter operative in a desired expression system, including, for example, a GAP promoter, an AOX1 promoter, a LAC4 promoter, a P350 hybrid promoter, a T7 promoter, a T5 promoter, a Ptac promoter, a Ptrc promoter, ParaBAD promoter, a PrhaBAD promoter, a Tet promoter or a PhoA phosphate-starvation promoter. 
     In the context of the present disclosure, “FCE” refers to a single-chain enzyme having RNA capping activity and having the amino acid sequence of positions 1 to 878 of SEQ ID NO:1. 
     In the context of the present disclosure, “FCE variant” (or “variant FCE”) refers to a non-naturally occurring, single-chain enzyme having (a) RNA capping activity and (b) less than 100% amino acid sequence identity to a naturally occurring single-chain RNA capping enzyme and/or a non-naturally occurring chemical modification (e.g., a polypeptide fused to its amino terminal or carboxy terminal end or other chemical modification). A variant amino acid sequence may have at least 80%, at least 85%, at least 90%, at least 95%, at least 97%, at least 98% or at least 99% identity to the amino acid sequence of FCE. Sequence differences may include insertions or deletions extending and/or shortening the N- and/or C-terminal ends. An FCE variant may have an amino acid sequence having less than 100% identity to positions 1 to 878 of SEQ ID NO: 1. An FCE variant may have, for example, an amino acid sequence having one or more substitutions with respect to positions 1 to 878 of SEQ ID NO: 1 and having at least 90%, at least 92%, at least 94%, at least 96%, or at least 98% identity with positions 1 to 878 of SEQ ID NO: 1. An FCE variant may have, for example, an amino acid sequence having one or more substitutions with respect to SEQ ID NO: 1 and having at least 90%, at least 92%, at least 94%, at least 96%, or at least 98% identity with SEQ ID NO: 1 or SEQ ID NO: 2. 
     An FCE variant may have an amino acid sequence having less than 100% identity to positions 1 to 878 of SEQ ID NO: 1. An FCE variant may have, for example, an amino acid sequence having one or more substitutions with respect to positions 389 to 1266 of SEQ ID NO: 2 and having at least 90%, at least 92%, at least 94%, at least 96%, or at least 98% identity with positions 389 to 1266 of SEQ ID NO: 2. FCE variants may comprise one or more substitutions that impact glycosylation of the protein. For example, an FCE variant may comprise one or more substitutions at one or more positions selected from positions corresponding to N215, N337, N572, N648, and N833 of SEQ ID NO: 1 or selected from positions corresponding to N603, N725, N960, N1036, and N1221 of SEQ ID NO: 2. Substitutions at positions corresponding to N215, N337, N572, N648, and N833 of SEQ ID NO: 1 and positions corresponding to N603, N725, N960, N1036, and N1221 of SEQ ID NO: 2 may be a deletion or any amino acid other than asparagine, but may be selected to retain one or more properties of the asparagine replaced. For example, replacement amino acids for asparagine may be glutamine In some embodiments, an FCE variant may comprise an amino acid sequence having (a) at least 90% identity to positions 1-214 of SEQ ID NO:1, (b) at least 90% identity to positions 216-336 of SEQ ID NO:1, (c) at least 90% identity to positions 338-571 of SEQ ID NO:1, (d) at least 90% identity to positions 573-647 of SEQ ID NO:1, (e) at least 90% identity to positions 649-832 of SEQ ID NO:1, (f) at least 90% identity to positions 834-878 of SEQ ID NO:1, and (g) a substitution at a position corresponding to position 215, 337, 572, 648, or 833 of SEQ ID NO: 1 (e.g., a deletion or any amino acid other than asparagine). In some embodiments, an FCE variant may comprise an amino acid sequence having (a) at least 90% identity to positions 389-602 of SEQ ID NO:2, (b) at least 90% identity to positions 604-724 of SEQ ID NO:2, (c) at least 90% identity to positions 726-959 of SEQ ID NO:2, (d) at least 90% identity to positions 961-1035 of SEQ ID NO:2, (e) at least 90% identity to positions 1037-1220 of SEQ ID NO:2, (f) at least 90% identity to positions 1222-1266 of SEQ ID NO:2, and (g) a substitution at a position corresponding to position 603, 725, 960, 1036, or 1221 of SEQ ID NO: 2 (e.g., a deletion or any amino acid other than asparagine). In some embodiments, an FCE variant may comprise a polypeptide having the amino acid sequence of SEQ ID NO:25 or SEQ ID NO:27. 
     In the context of the present disclosure, “in vitro transcription” (IVT) refers to a cell-free reaction in which a DNA template is copied by a DNA-directed RNA polymerase (typically a bacteriophage polymerase) to produce a product that comprises one or more RNA molecules that have been copied from the template. 
     In the context of the present disclosure, “modified nucleotide” refers to nucleotides having a modification on the sugars (e.g., 2′-fluororibose, ribose, 2′-deoxyribose, arabinose, and hexose); and/or in the phosphate groups (e.g., phosphorothioates and 5′-N-phosphoramidite linkages); and/or in the nucleotide base (e.g., as described in U.S. Pat. No. 8,383,340; WO 2013/151666; U.S. Pat. No. 9,428,535 B2; US 2016/0032316). 
     In the context of the present disclosure, “non-naturally occurring” refers to a polynucleotide, polypeptide, carbohydrate, lipid, or composition that does not exist in nature. Such a polynucleotide, polypeptide, carbohydrate, lipid, or composition may differ from naturally occurring polynucleotides polypeptides, carbohydrates, lipids, or compositions in one or more respects. For example, a polymer (e.g., a polynucleotide, polypeptide, or carbohydrate) may differ in the kind and arrangement of the component building blocks (e.g., nucleotide sequence, amino acid sequence, or sugar molecules). A polymer may differ from a naturally occurring polymer with respect to the molecule(s) to which it is linked. For example, a “non-naturally occurring” protein may differ from naturally occurring proteins in its secondary, tertiary, or quaternary structure, by having a chemical bond (e.g., a covalent bond including a peptide bond, a phosphate bond, a disulfide bond, an ester bond, and ether bond, and others) to a polypeptide (e.g., a fusion protein), a lipid, a carbohydrate, or any other molecule. Similarly, a “non-naturally occurring” polynucleotide or nucleic acid may contain one or more other modifications (e.g., an added label or other moiety) to the 5′-end, the 3′ end, and/or between the 5′- and 3′-ends (e.g., methylation) of the nucleic acid. A “non-naturally occurring” composition may differ from naturally occurring compositions in one or more of the following respects: (a) having components that are not combined in nature, (b) having components in concentrations not found in nature, (c) omitting one or components otherwise found in naturally occurring compositions, (d) having a form not found in nature, e.g., dried, freeze dried, crystalline, aqueous, and (e) having one or more additional components beyond those found in nature (e.g., buffering agents, a detergent, a dye, a solvent or a preservative). 
     In the context of the present disclosure, “polymerase” refers to an enzyme that synthesizes a polynucleotide from NTPs with or without a template. Examples of enzymes include T3 RNA polymerase, T7 RNA polymerase, SP6 polymerase, among others and variants thereof including thermostable variants (e.g., International Application No. PCT/US2017/013179 and U.S. application Ser. No. 15/594,090). 
     In the context of the present disclosure, a “single-chain RNA capping enzyme” refers to a capping enzyme in which a single polypeptide chain as a monomer displays RNA triphosphatase (TPase), guanylyltransferase (GTase) and guanine-N7 methyltransferase (N7 MTase) activities. Faustovirus, mimivirus and moumouvirus capping enzymes are examples of single-chain RNA capping enzymes. For clarity, VCE is a heterodimer and, as such, is not a single-chain RNA capping enzyme. 
     In the context of the present disclosure, a “substitution” at a position in a comparator amino acid sequence refers to any difference at that position relative to the corresponding position in a reference sequence, including a deletion, an insertion, and a different amino acid, where the comparator and reference sequences are at least 80% identical to each other. A substitution in a comparator sequence, in addition to being different than the reference sequence, may differ from all corresponding positions in naturally occurring sequences that are at least 80% identical to the comparator sequence. 
     In the context of the present disclosure, “transcript” refers to a polynucleotide template for a polypeptide. A transcript may comprise RNA (e.g., ssRNA), a cap or cap analog, and/or a polyA tail. A transcript may be capable of translation in a cell (e.g., a bacterial cell and/or a yeast cell). For example, a transcript may be or comprise mRNA. A fusion transcript may comprise polynucleotide templates for two or more polypeptides in a single polynucleotide. 
     In the context of the present disclosure, “uncapped” refers to a condition of an RNA in which it does not have a cap structure at its 5′ end. Uncapped RNA typically has a tri-phosphoryl, di-phosphoryl, mono-phosphoryl or a hydroxyl group at the 5′ end. 
     All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference. All reagents referenced, if unavailable elsewhere, may be obtained from the indicated source and/or New England Biolabs, Inc. (Ipswich, Mass.). 
     Production of stable mRNA capable of efficient translation upon introduction to a subject may require an appropriate cap structure. In addition, a cap may avoid triggering the innate immune response observed upon introduction of uncapped (5′ -triphosphate) RNAs (Pichlmair, et al.,  Science  2006 314: 997-1001; Diamond, et al.,  Cytokine  &amp;  Growth Factor Reviews,  2014 25: 543-550). As such, it may be desirable to add a cap to synthetic RNA in many therapeutic applications (e.g., protein replacement therapy as well as prophylactic or therapeutic vaccination). 
     Vaccinia virus, like most viruses, has a robust set of mechanisms to co-opt host cell machinery for the production of viral proteins. One such tool is the vaccinia capping enzyme, which forms a Cap 0 structure (m7Gppp5′N) at the 5′ end of uncapped RNA molecules through its RNA triphosphatase, guanylyltransferase, and guanine methyltransferase activities. In cells, capping viral transcripts allows them to be transcribed by the infected cells. Other transcripts may be capped rapidly in vitro in the presence of the vaccinia capping enzyme, reaction buffer, GTP, and the methyl donor, SAM. Production of active vaccinia capping enzyme for cell-free vaccine production can be challenging. Properties of VCE may impede production (e.g., high capacity production) and use of the enzyme. For example, efforts to express the vaccinia virus D1R gene in bacteria and yeast as a means to produce and recover the 97 kDa subunit result in poor yields, possibly due, at least in part, to the insolubility and/or hydrophobicity of the 97 kDa subunit. In addition, in vitro assembly of the small and large subunits into a whole protein may yield an enzyme with little to no catalytic activity. Separately produced subunits may not be present in an appropriate ratio or conformation to efficiently or productively bind to one another and/or bind to substrates. Accordingly, a need has arisen for alternatives to VCE for efficient enzymatic capping or RNA molecules. 
     The present disclosure relates to RNA capping enzymes from Faustovirus and variants thereof (e.g., variants across strains of Faustovirus and variants from related viruses) and kits including these enzymes. The present disclosure further relates to methods of making and using such enzymes. For example, the present disclosure provides FCE and variants thereof. An FCE variant may comprise a non-naturally occurring amino acid sequence that is at least 90% identical (e.g., at least 92% identical, at least 94% identical, at least 96% identical, at least 98% identical) to positions 1-878 of SEQ ID NO: 1 or at least 90% identical (e.g., at least 92% identical, at least 94% identical, at least 96% identical, at least 98% identical) to SEQ ID NO: 1 or at least 90% identical (e.g., at least 92% identical, at least 94% identical, at least 96% identical, at least 98% identical) to positions 389 to 1266 of SEQ ID NO: 2 or at least 90% identical (e.g., at least 92% identical, at least 94% identical, at least 96% identical, at least 98% identical) to SEQ ID NO: 2. An FCE variant may be fused to one or more peptides (e.g., sorting signals, His, MBP or other purification tags) or polypeptides (e.g., other enzymes, linkers or spacers). In some embodiments, an FCE variant may be immobilized, for example, to a solid support (e.g., magnetic, agarose, polystyrene, polyacrylamide, chitin). 
     In some embodiments, a composition may include one or more FCE variants, one or more substrates of the one or more FCE variants (e.g., uncapped RNA, GDP), one or more intermediates or products (e.g., inorganic phosphate, inorganic diphosphate) of the one or more FCE variants, one or more transcripts of one or more FCE variants (e.g., a capped FCE variant transcript), and any combination thereof. A composition may include, according to some embodiments, an FCE variant and one or more additional components that support storage, transportation, activity and/or use of such FCE variant. For example, a composition may comprise an FCE variant and an uncapped ribonucleic acid (e.g., an uncapped therapeutic RNA), dNTPs, rNTPs, primers, other enzymes (e.g., decapping enzymes, polymerases, or other enzymes), buffering agents (e.g., a storage buffer, a reaction buffer), or combinations thereof. Uncapped RNA may be synthesized using solid-phase oligonucleotide synthesis chemistry or by transcribing a DNA template using a polymerase (e.g., a bacteriophage polymerase) in an in vitro transcription reaction, for example. In some embodiments, a composition may comprise SAM and/or a cap 2′O methyltransferase enzyme (2′OMTase). 
     A composition may comprise one or more additives (e.g. glycerol), salts (e.g. KCl), reducing agents, chelating agents (e.g., EDTA), detergents, and/or denaturants (e.g., caffeine, urea), among others. A composition comprising dNTPs may include one, two, three or all four of dATP, dTTP, dGTP and dCTP. A composition comprising rNTPs may include one, two, three of all four or rATP, rUTP, rGTP and rCTP. A composition may further comprise one or more modified nucleotides. A composition may comprise one or more modified nucleotides. A composition may optionally comprise one or more primers (random primers, bump primers, exonuclease-resistant primers, chemically-modified primers, custom sequence primers, or combinations thereof). Compositions optionally may comprise one or more of the components set forth below for kits. In some embodiments, a composition may be glycerol-free, may be dry (e.g., as a result of lyophilization), and/or may be aqueous. 
     A composition may be formulated for delivery to a subject (e.g., a human subject, a non-human animal subject). A composition, for example, a composition including one or more products of an FCE variant, may be free of materials (e.g., enzymes) derived from non-human animals according to some embodiments. 
     Methods 
     According to some embodiments, a capping method may comprise contacting a single-chain RNA capping enzyme (e.g., FCE, an FCE variant) with one or more of a target RNA (e.g., an uncapped therapeutic RNA), an NTP, a modified NTP, a cap, S-adenosylmethionine (SAM), and a buffering agent to form a reaction mix. This contact may be at a sufficient temperature and for a sufficient time to form a capped target RNA. For example, the contact may be at a temperature (e.g., constant or varying) in the range of 37° C. -60° C. and/or for a time in the range of seconds to hours (e.g., from 60 seconds to 16 hours). The contacting may be RNase free and/or may further include contacting the other components with an RNase inhibitor. The contacting may further comprise contacting the other components with a cap 2′O methyltransferase enzyme (2′OMTase). 
     A single-chain RNA capping enzyme for a capping method may comprise an amino acid sequence that is at least 90% identical (e.g., at least 92% identical, at least 94% identical, at least 96% identical, at least 98% identical) to positions 1-878 of SEQ ID NO: 1 or at least 90% identical (e.g., at least 92% identical, at least 94% identical, at least 96% identical, at least 98% identical) to SEQ ID NO: 1 or at least 90% identical (e.g., at least 92% identical, at least 94% identical, at least 96% identical, at least 98% identical) to positions 389 to 1266 of SEQ ID NO: 2 or at least 90% identical (e.g., at least 92% identical, at least 94% identical, at least 96% identical, at least 98% identical) to SEQ ID NO: 2. A capping method may further comprise monitoring the appearance capped target RNA. Capped RNA may be monitored/detected by denaturing urea polyacrylamide gel electrophoresis, radiometric assays, capillary electrophoresis, or mass spectrometry-based methods (e.g., as provided by Beverly, M., Dell, A., Parmar, P., and Houghton, L. 2016. Label-free analysis of mRNA capping efficiency using RNase H probes and LC-MS.  Analytical and bioanalytical chemistry  408:5021-5030). 
     A capping method, in some embodiments, may comprise (a) contacting a polymerase with one or more of a polynucleotide template (DNA or RNA) encoding a target RNA, rNTPs and/or modified rNTPs, and a buffer to form a transcription product comprising the target RNA and (b) contacting a single-chain RNA capping enzyme (e.g., FCE, an FCE variant) with one or more of the transcription products, an NTP, a modified NTP, a cap, S-adenosylmethionine (SAM), and a buffering agent to form a reaction mix. This contact may be at a sufficient temperature and for a sufficient time to form a capped target RNA. For example, the contact may be at a temperature (e.g., constant or varying) in the range of 37° C. -60° C. and/or for a time in the range of second to hours (e.g., from 60 seconds to 16 hours). 
     A capping method may further comprise contacting the capped RNA with a one or more pharmaceutically acceptable additives (e.g., excipients, diluents, and/or carriers), including, for example, fluids, solvents, dispersion media, wetting agents, crowding agents, micelles, lipidoids, liposomes, polymers, lipoplexes, peptides, proteins, salts, surface active agents, isotonic agents, thickeners, emulsifiers, preservatives, stabilizers, solubilizers, buffers, sugars, starches, cellulose, waxes, glycols, polyols, polyesters, polycarbonates, polyanhydrides, hyaluronidase, nanoparticles (e.g., lipid nanoparticles, core-shell nanoparticles, and/or nanoparticle mimics), and combinations thereof. In some embodiments, pharmaceutically acceptable additives protect, preserve, and/or stabilize a capped RNA during manufacture, storage, and/or administration to a subject. Examples of pharmaceutical acceptable additives include those described in U.S. Patent Publication No. 2017/0119740. A capping method may further comprise contacting the capped RNA with one or more additives selected from lipidoids, liposomes, polymers, lipoplexes, peptides, proteins, cells transfected with HCMV RNA vaccines (e.g., for transplantation into a subject), hyaluronidase, nanoparticles (e.g., lipid nanoparticles, core-shell nanoparticles, and/or nanoparticle mimics). 
     Capped RNAs may be formulated for delivery and/or delivered to a eukaryotic organism. Examples of subjects that may receive a capped RNA include humans and non-human animals (e.g., mouse, rat, rabbit, dog, cat, cattle, swine, sheep, horse or primate). Capped RNAs may be delivered to plants or plant cells, according to some embodiments, to confer or augment resistance to or tolerance of an environmental condition (e.g., drought, salt) and/or to prevent, mitigate or treat herbivory, pathogen infection, or the effects thereof. Capped RNA also may be delivered to one or more yeast cells. 
     In some embodiments, the present disclosure provides methods for preparing a capped RNA dosage form comprising, contacting an uncapped RNA with an FCE variant to form a capped RNA, and contacting the capped RNA with one or more pharmaceutically acceptable additives, binders, buffers, coatings, colors, controlled release agents, delivery agents (e.g., liposomes, propellants), diluents, disintegrants, dyes, excipients, fillers, lipids, lubricants, salts, sorbants, stabilizers, and/or other agents to produce an RNA dosage form. A capped RNA may be combined (e.g., in a single dosage form or delivered concurrently or in sequence with one or more other active pharmaceutical agents. A capped RNA and/or its encoded translation product(s) may function in a subject as an active pharmaceutical agent, according to some embodiments. A capped RNA (e.g., a capped RNA dosage form) may be administered by any suitable route of administration, including transdermal, oral, enteral, parenteral, ocular, ottic, transmucosal, sublingual, and pulmonary (e.g., by nebulization and/or inhalation) routes, and combinations thereof. 
     Capped RNA can either be naked or formulated in a suitable form for delivery to a subject, e.g., a human Formulations can include liquid formulations (solutions, suspensions, dispersions), topical formulations (gels, ointments, drops, creams), liposomal formulations (such as those described in: U.S. Pat. No. 9,629,804 B2; US 2012/0251618 A1; WO 2014/152211; US 2016/0038432 A1). The cells into which the RNA product is introduced may be in vitro (i.e., cells that have been cultured in vitro on a synthetic medium). Accordingly, the RNA product may be transfected into the cells. The cells into which the RNA product is introduced may be in vivo (cells that are part of a mammal). The cells into which the RNA product is introduced may be present ex vivo (cells that are part of a tissue, e.g., a soft tissue that has been removed from a mammal or isolated from the blood of a mammal). 
     Methods for production of an FCE variant may comprise, for example, contacting a polynucleotide encoding such FCE variant with an expression system (e.g., a bacterial expression system, a yeast expression system, an insect expression system, a mammalian expression system, a viral expression system or a cell-free expression system). A method of producing an FCE variant may comprise contacting an uncapped FCE variant transcript with a capping enzyme (e.g., vaccinia capping enzyme, FCE, an FCE variant) to form a capped FCE variant transcript. A method may further include contacting a capped FCE variant transcript with an expression system to form FCE protein. 
     An FCE variant protein may be produced, according to some embodiments, by constructing an expression plasmid compatible to  E. coli  or yeast expression systems under the control of an appropriate promoter. The plasmid can be introduced into the cells via transformation and the resultant  E. coli  or yeast strain can be cultured using appropriate methods. The expression of the FCE variant protein can be induced by subjecting the culture to appropriate conditions in case of inducible promoters or by following appropriate culture conditions for auto-induced promoters. Cultivation conditions (e.g., time, temperature, media composition) may be maintained or adjusted as needed to express the FCE protein variant. Cultures may be harvested, for example, by centrifugation or tangential flow filtration. Harvested cells (e.g., in the form of pellets) may be stored at low temperatures or lysed using an appropriate method such as sonication or mechanical sheering. Lysates may be clarified, for example, by centrifugation or tangential flow filtration. The FCE variant protein may be purified from the clarified lysate or spent culture medium, for example, by chromatographic methods. 
     In some embodiments, an FCE variant protein may be produced by contacting an FCE variant protein expression DNA construct operably linked to an expression control sequence (e.g., an appropriate promoter) to an in vitro transcription/translation system such as PURExpress In vitro Protein Synthesis Kit (New England Biolabs, Inc.) or TnT Quick Coupled Transcription/Translation System (Promega). In addition, an FCE variant protein can be produced by contacting an FCE variant protein expression DNA construct under the control of an appropriate promoter to a cell-free protein synthesis system derived from organisms such as  E. coli  (e.g., NEBExpress Cell-free  E. coli  Protein Synthesis System (New England Biolabs, Inc.), rabbit, wheat germ, insect, or human. Reaction conditions (e.g., time, temperature, reaction composition) may be maintained or adjusted as needed to express the FCE protein variant. Expressed variant protein may be purified by appropriate methods (e.g., chromatographic methods). 
     Kits 
     The present disclosure further relates to kits including an FCE variant. For example, a kit may include an FCE variant and an uncapped ribonucleic acid, dNTPs, rNTPs, primers, other enzymes (e.g., decapping enzymes, polymerases, or other enzymes), buffering agents, or combinations thereof. An FCE variant may be included in a storage buffer (e.g., comprising glycerol and a buffering agent). A kit may include a reaction buffer which may be in concentrated form, and the buffer may contain additives (e.g. glycerol), salt (e.g. KCl), reducing agent, EDTA or detergents, among others. A kit comprising dNTPs may include one, two, three or all four of dATP, dTTP, dGTP and dCTP. A kit comprising rNTPs may include one, two, three of all four or rATP, rUTP, rGTP and rCTP. A kit may further comprise one or more modified nucleotides. A kit may optionally comprise one or more primers (random primers, bump primers, exonuclease-resistant primers, chemically-modified primers, custom sequence primers, or combinations thereof). One or more components of a kit may be included in one container for a single step reaction, or one or more components may be contained in one container, but separated from other components for sequential use or parallel use. The contents of a kit may be formulated for use in a desired method or process. 
     A kit is provided that contains: (i) an FCE variant; and (ii) a buffer. An FCE variant may have a lyophilized form or may be included in a buffer (e.g., a storage buffer or a reaction buffer in concentrated form). A kit may contain an FCE variant in a mastermix suitable for receiving and capping a template ribonucleic acid. An FCE variant may be a purified enzyme so as to contain no other detectable enzyme activities. The reaction buffer in (ii) and/or storage buffers containing an FCE variant in (i) may include non-ionic, ionic e.g. anionic or zwitterionic surfactants, denaturants, and/or crowding agents. A kit may include an FCE variant and the reaction buffer in a single tube or in different tubes. 
     A subject kit may further include instructions for using the components of the kit to practice a desired method. The instructions may be recorded on a suitable recording medium. For example, instructions may be printed on a substrate, such as paper or plastic, etc. As such, the instructions may be present in the kits as a package insert, in the labeling of the container of the kit or components thereof (i.e., associated with the packaging or sub-packaging) etc. Instructions may be present as an electronic storage data file residing on a suitable computer readable storage medium (e.g., a CD-ROM, a flash drive). Instructions may be provided remotely using, for example, cloud or internet resources with a link or other access instructions provided in or with a kit. 
     EXAMPLES 
     Some specific example embodiments may be illustrated by one or more of the examples provided herein. 
     EXAMPLE 1: Plasmids and Expression Cassettes 
     EXAMPLE 1A. Construction of  P. pastoris  FCE Expression Vectors for Secreted Expression 
     The gene encoding the mRNA capping enzyme, FCE containing a C-terminal 8× Histidine tag, was amplified by PCR using the forward and reverse primers, respectively: 
     
       
         
           
               
               
            
               
                   
                 (SEQ ID NO: 3) 
               
               
                   
                 5′ agaaaagagaggccgaagctGCGAAGCGTCTGCAGCGT, 
               
               
                   
                 and 
               
               
                   
                   
               
               
                   
                 (SEQ ID NO: 4) 
               
               
                   
                 5′ cctcttgagcggccgcccctTTAGTGGTGGTGGTGGTGG. 
               
            
           
         
       
     
     The forward and reverse primers were engineered to contain sequences that overlap the pD912(GAP) vector (lower case) ( FIG. 1A ). The NEBuilder Assembly Tool was used for primer and assembly design. The 2661 bp FCE gene was amplified from the plasmid pFCE-CHis8 containing the full-length gene and 8× Histidine tag, using Q5 High-Fidelity 2× Master Mix (New England Biolabs). The pD912(GAP) was prepared from pD912(AOX) vector by replacing 462 bp long AOX1 promoter sequence with 483 bp long DNA fragment containing  Pichia pastoris  GAP promoter. The 3826 bp vector fragment was amplified from the plasmid pD912(GAP) by PCR using the forward and reverse primers, respectively: 
     
       
         
           
               
               
            
               
                   
                 (SEQ ID NO: 5) 
               
               
                   
                 5′ AGGGGCGGCCGCTCAAGA, 
               
               
                   
                 and 
               
               
                   
                   
               
               
                   
                 (SEQ ID NO: 6) 
               
               
                   
                 5′ AGCTTCGGCCTCTCTTTTC. 
               
            
           
         
       
     
     This integrative expression vector contains the mating factor alpha secretion leader for extracellular expression, the GAP1 promoter which initiates and terminates transcription and the zeocin resistance gene which allows for selection of transformants by growth on zeocin-containing medium. The two fragments were joined using NEBuilder HiFi DNA Assembly Master Mix (New England Biolabs). 2 μl of the reaction was transformed into 50 μl of NEB 5-alpha Competent  E. coli  (High Efficiency) cells, plated on LB-zeocin (25 μg/mL) plates and incubated overnight at 37° C. resulting in a  P. pastoris  expression vector pD912(GAP)-FCE(WT)-8His (SEQ ID NO:1) ( FIG. 2 ). 
     For the construction of asparagine-linked (N-linked) glycan variants of FCE, the potential N-linked glycosylation sites were first identified using the NetNGlyc 1.0 server (www.cbs.dtu.dk/services/NetNGlyc/). The prediction results indicated 5 potential sites at amino acid sequence positions 215, 337, 572, 648, and 833. Positions 215, 337 and 572 scored above the N-glycosylation threshold potential. In light of these predictions, 2 variant constructs were generated, one with N215Q, N337Q, N572Q, N648Q, and N833Q substitutions, and the other with N215Q, N337Q and N572Q substitutions. The Q5 Site Directed Mutagenesis Kit (New England Biolabs, Inc.) was used for construction of the variant expression vectors. The NEBaseChanger tool was used for primer design. The primers for each variant are listed below: 
     
       
         
           
               
               
               
             
               
                   
               
               
                   
                   
                 SEQ  
               
               
                   
                   
                 ID  
               
               
                 Name 
                 Sequence 
                 NO 
               
               
                   
               
             
            
               
                 N215Q-Fwd 
                 5′ TCGTAACGCGcaaAGCACCGCGG 
                  7 
               
               
                   
               
               
                 N215Q-Rev 
                 5′ ACGCTGCTCAGCAGCTCCAC 
                  8 
               
               
                   
               
               
                 N337Q-Fwd 
                 5′ TATCATTAGCcaaAACACCCAGGTTTATAC 
                  9 
               
               
                   
               
               
                 N337Q-Rev 
                 5′ ACGTCGAACACGTACAGA 
                 10 
               
               
                   
               
               
                 N572Q-Fwd 
                 5′ CTTCGAGAAGcaaAAAAGCGATATCTATG 
                 11 
               
               
                   
               
               
                 N572Q-Rev 
                 5′ TAGCCCGGGTTATACTTG 
                 12 
               
               
                   
               
               
                 N648Q-Fwd: 
                 5′ ACCGGCTACcaaAAGAGCCACCGTGGCGGT 
                 13 
               
               
                   
               
               
                 N648Q-Rev: 
                 5′ GTGGCTCTTTTGGTAGCCGGTAATCTCGTT 
                 14 
               
               
                   
               
               
                 N833Q-Fwd: 
                 5′ GAAAGCGCGcaaTTCAGCGTGCTGTACGAG 
                 15 
               
               
                   
               
               
                 N833Q-Rev: 
                 5′ CACGCTGAATTGCGCGCTTTCAACCAGATC 
                 16 
               
               
                   
               
            
           
         
       
     
     The forward primers contained the nucleotide sequence encoding the glutamine residue (lower case). The FCE gene containing a single mutated N-linked site was amplified from the plasmid pD912(GAP)-FCE-8His using Q5 High-Fidelity 2× Master Mix (New England Biolabs). The pD912 (P GAP ) vector fragment, containing the  S. cerevisae  α-mating factor pre-pro signal sequence, was also amplified by Q5 High-Fidelity 2× Master Mix using the primers described above. Each FCE fragment was joined to the pD912 (GAP) vector fragment using NEBuilder HiFi DNA Assembly Master Mix. This resulted in the three plasmids, pD912(GAP)-FCE(N215Q)-8His, pD912(GAP)-FCE(N337Q)-8His and pD912(GAP)-FCE (N572Q)-8His. All plasmids were sequence verified to contain the correct mutations. 
     A plasmid containing three N-glycan variants was created by amplifying the 708 bp fragment from N337 to N572 and assembling the resulting PCR product into the pD912(GAP)-FCE(N215Q)-8His plasmid using NEBuilder HiFi DNA Assembly Mix. This resulted in the plasmid, pD912(GAP)-FCE(N215Q/N337Q/N572Q)-8His (SEQ ID NO:24). 
     A plasmid containing all five N-glycan variants was created by amplifying the 557 bp fragment from N648 to N833 and assembling the resulting PCR product into the pD912(GAP)-FCE(N215Q/N337Q/N572Q)-8His plasmid using NEBuilder HiFi DNA Assembly Mix. This resulted in the plasmid, pD912(GAP)-FCE(N215Q/N337Q/N572Q/N648Q/N833Q)-8His (SEQ ID NO:24). Double variants of N215Q/N337Q and N215Q/N572Q were constructed using the Q5 Site Directed Mutagenesis Kit as described above resulting in the plasmids, pD912(GAP)-FCE(N215Q/N337Q)-8His and pD912(GAP)-FCE(N215Q/N572Q)-8His. 
     EXAMPLE 1B. Construction of  K. lactis  FCE Expression Vectors for Cytoplasmic Expression 
     The gene encoding the mRNA capping enzyme, FCE containing a C-terminal 8× Histidine tag, was amplified by PCR using the forward and reverse primers, respectively: 
                            (SEQ ID NO: 17)           5′ tcggggatgacgatgacaagGCGAAGCGTCTGCAGCGT           and                       (SEQ ID NO: 18)           5′ tcagcctctcttttctcgagTTAGTGGTGGTGGTGGTGG.            
The forward and reverse primers were engineered to contain sequences that overlap the pKLMF-EK vector (New England Biolabs) (lower case) ( FIG. 1B ). The NEBuilder Assembly Tool was used for primer and assembly design. The 2661 bp FCE gene was amplified from the plasmid pFCE-CHis8 (Siuhong Chan) containing the full-length gene and 8× Histidine tag, using Q5 High-Fidelity 2× Master Mix (New England Biolabs).
 
     The 10028 bp vector fragment was amplified from the plasmid (CT867) pKLMF-A313V-EK-LongerLinker (unoptimized) by Q5 High-Fidelity 2× Master Mix using the forward and reverse primers, respectively: 
                            (SEQ ID NO: 19)           5′ CTCGAGAAAAGAGAGGCTGAAGCT           and                       (SEQ ID NO: 20)           5′ CTTGTCATCGTCATCCCCGAG.            
This integrative expression vector contains the malE gene which encodes for maltose binding protein (MBP), the LAC4 promoter which initiates and terminates transcription and the acetamidase gene which allows for selection of transformants by growth on acetamide-containing medium. In this vector,  K. lactis  α-mating factor pre-pro signal sequence has been replaced with the malE gene. Thus MBP-fusion proteins will not be directed to the secretory pathway but instead will be retained in the yeast cytosol. The two fragments were joined using NEBuilder HiFi DNA Assembly Master Mix (New England Biolabs). The assembled linear expression cassette ( FIG. 2 ) was amplified by PCR using the forward and reverse primers, respectively (SEQ ID NO:2):
 
     
       
         
           
               
               
            
               
                   
                 (SEQ ID NO: 21) 
               
               
                   
                 5′ GATCGACTCATAAAATAGTAACC 
               
               
                   
                 and 
               
               
                   
                   
               
               
                   
                 (SEQ ID NO: 22) 
               
               
                   
                 5′ CCGCGGAAATTTAGGAATTTTAAAC. 
               
            
           
         
       
     
     EXAMPLE 2: Yeast Transformation and Expression 
       Pichia pastoris  aoxlΔ(MutS) (ATUM, formerly DNA 2.0) and  Kluyveromyces lactis  GG799 (New England Biolabs) strains were for each relevant experiment. Electrocompetent cells were prepared using the lithium acetate/DTT method (Wu and Letchworth, 2004). Electroporation conditions were 1.5 KV, 25 μF and 200 Ohm using a 0.2 cm cuvette followed by selection of transformants by growth on yeast peptone dextrose (YPD) agar medium supplemented with 1 M sorbitol and 500 μg/mL Zeocin (Teknova) ( P. pastoris ) and yeast carbon base (YCB) supplemented with 5 mM acetamide ( K. lactis ) and incubated for 3-4 days at 30° C. 
     Three micrograms  P. pastoris  expression plasmids were linearized by SacI-HF restriction digestion and the purified products were used to transform electrocompetent  P. pastoris  MutS cells. 0.5 μg purified  K. lactis  linear expression cassette generated by PCR, was used to transform electrocompetent  K. lactis  GG799 cells. 
     Eight to twelve transformants were patched onto fresh selection plates and incubated for an additional 1-2 days at 30° C. For the identification of transformants by PCR, genomic DNA was isolated from each strain using lithium acetate/sodium dodecyl sulfate (LiOAc/SDS) method (Lõoke et al., 2011). PCR was used to identify transformants having an integrated expression cassette. 
     EXAMPLE 3: Yeast Culture Conditions and Expression 
     For  Pichia pastoris  constructs (containing GAP promoter), transformants were grown at 30° C. in 5 mL of BMGY-Buffered Glycerol Complex Medium (Teknova) (1% yeast extract, 2% tryptone, 1.34% yeast nitrogen base (YNB) without amino acids with ammonium sulfate, 0.0004% biotin, 1% glycerol as the carbon source, 100 mM potassium phosphate, pH 6.0). After 48 hours, the spent culture media was harvested. 
     For  Kluyveromyces lactis  constructs (containing LAC4 promoter), transformants were grown at 30° C. in 5 mL of yeast medium (1% yeast extract, 2% peptone) supplemented with 2% galactose as the carbon source. After 48 hours, the cells were harvested. 
     EXAMPLE 4: Analysis of Cultures 
     The spent culture media ( P. pastoris  constructs) were buffer-exchanged in 50 mM Tris-HC1, pH 7.5 buffer containing 300 mM NaCl and concentrated ten-fold using Vivaspin 30 kDa MWCO filters (Sartorius). To assess the extent of glycosylation, the concentrated spent culture media were subject to Endo Hf (New England Biolabs) digestions under native conditions in the presence of 1× GlycoBuffer 3 (50 mM sodium acetate, pH 6.0). 
     FCE proteins (wild-type and N-glycan variants) were purified from the concentrated spent cultures using NEBExpress Ni Spin Columns (New England Biolabs). The columns were washed twice with 50 mM Tris-HCl, pH 7.5 buffer containing 300 mM NaCl and 5 mM imidazole then once with 50 mM Tris-HCl, pH 7.5 buffer containing 300 mM NaCl and 10 mM imidazole. The purified protein was eluted with 50 mM Tris-HCl, pH 7.5 buffer containing 300 mM NaCl and 500 mM imidazole. 
     To prepare cell lysates ( K. lactis  constructs), cells were resuspended in 50 mM Tris-HCl, pH 7.5 buffer containing 300 mM NaCl and sonicated (Qsonica). The soluble cell lysate was pre-cleared by centrifugation at 16000×g for 15 minutes at 4° C. The cell lysates and spent culture media were analyzed by SDS-PAGE on 4-20% polyacrylamide gel, followed by western blotting with a His-tag antibody (Thermo Fisher Scientific). 
     EXAMPLE 5: In Vitro mRNA Capping Assay 
     In vitro capping reactions were carried out in a 10 μL reaction containing 1× capping buffer (50 mM Tris pH 8.0, 5 mM KCl, mM MgCl 2 , 1 mM DTT) supplemented with 0.1 mM S-adenosylmethionine, 0.5 mM GTP, 500 nM substrate RNA (SEQ ID NO: 23: 5′-GUAGAACUUCGUCGAGUACGCUCAA[FAM]-3′, Bio-Synthesis, Inc.), and spent culture medium of cell lysate at 37° C. for 30 minutes. Reactions were stopped by adding 10 μL of quenching solution (20 mM EDTA, 2% SDS). Reactions were diluted in nuclease-free water to reach a final substrate concentration of 5 nM before capillary electrophoresis on either an Applied Biosystems 3130×1 Genetic Analyzer (16 capillary array) or an Applied Biosystems 3730×1 Genetic Analyzer (96 capillary array) using GeneScan 120 LIZ dye Size Standard (Applied Biosystems). Reaction products were analyzed using PeakScanner software (Thermo Fisher Scientific). 
     EXAMPLE 6: Production of Glycosylated FCE 
     Western blot analysis of the transformants expressing FCE indicated that the recombinant fusion protein is secreted in the media from  Pichia pastoris  cells. The results also indicated, that the protein is glycosylated as evidenced by the mobility shift and removal of smears after EndoHf digestion. Variant N215Q shows significant reduction in glycosylation while variants N337Q and N572Q show a slight reduction in glycosylation as compared to wild type ( FIG. 3A  and  FIG. 3B ). 
     The full-length FCE is also expressed as a single polypeptide in the  K. lactis  cytoplasm ( FIG. 3B ). All recombinants displayed mRNA capping activity both before and after EndoHf digestion ( FIG. 4A  and  FIG. 4B ). 
     After nickel spin column purification of wild type FCE and mutants expressed from  Pichia pastoris  cells, the load (spent culture media) and elution fractions were analyzed by SDS-PAGE. The eluted FCE (N215Q/N337Q/N572Q) mutant shows a significant decrease in glycosylation as observed by the improved band resolution as compared to wild type. The purified FCE (N215Q/N337Q/N572Q/N648Q/N833Q) mutant shows further improved band resolution, indicating a further decrease in glycosylation ( FIG. 5 ). The concentrated spent culture media from all 3 recombinants showed mRNA capping activity ( FIG. 6 ). 
     Further SDS-PAGE analysis and Western blot analysis following EndoHf treatment of wild type FCE, FCE (N215Q/N337Q/N572Q) and FCE (N215Q/337Q/ N572Q/N648Q/N833Q) spent culture confirmed the reduction or elimination of glycosylation of the secreted protein ( FIG. 7A  and  FIG. 7B ). 
     REFERENCES 
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     Diamond, et al., Cytokine &amp; Growth Factor Reviews, 2014 25: 543-550. 
     Kore, Nucleosides, Nucleotides, and Nucleic Acids, 2006, 25: 15 307-14. 
     Kore, Nucleosides, Nucleotides, and Nucleic Acids, 2006, 25: 337-40. 
     Lõoke, M., Kristjuhan, K., &amp; Kristjuhan, A. (2011). Extraction of genomic DNA from yeasts for PCR-based applications.  BioTechniques,  50(5), 325-328. 
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     Ramanathan, Nucleic Acids Res. 2016 44: 7511-7526. 
     Sakhtah H, Behler J, Ali-Reynolds A, Causey T B, Vainauskas S, Taron C H. 2019. A novel regulated hybrid promoter that permits autoinduction of heterologous protein expression in  Kluyveromyces lactis . Appl Environ Microbiol 85:e00542-19. doi.org/10.1128/AEM.00542-19. 
     Shuman S, 1989, Functional domains of vaccinia virus mRNA capping enzyme. Analysis by limited tryptic digestion. J Biol Chem Jun 5; 264(16):9690-5. 
     Wu, S., &amp; Letchworth, G. J. (2004). High efficiency transformation by electroporation of  Pichia pastoris  pretreated with lithium acetate and dithiothreitol.  BioTechniques,  36(1), 152-154.