The mRNA Cap 2′-O-methyltransferase is a recombinant protein derived from vaccinia virus, it can add a methyl group to the 2'-O at the 5' end of the RNA immediately adjacent to the first nucleotide of the cap structure. This enzyme utilizes S-adenosylmethionine （SAM） as a methyl donor to methylate capped Cap 0 to Cap 1. Cap 1 structure can enhance the translation efficiency of mRNA and reduce the immunogenicity of mRNA structure itself, so it helps to improve the expression level of encoded protein after mRNA transfection.