In enzymology, a mRNA (nucleoside-2'-O-)-methyltransferase (EC 2.1.1.57) is an enzyme that catalyzes the chemical reaction

S-adenosyl-L-methionine + m₇G(5')pppR-RNA ${\displaystyle \rightleftharpoons }$ S-adenosyl-L-homocysteine + m₇G(5')pppRm-RNA (mRNA containing a 2'-O-methylpurine cap)

Thus, the two substrates of this enzyme are S-adenosyl methionine and m7G(5')pppR-RNA, whereas its two products are S-adenosylhomocysteine and m7G(5')pppRm-RNA (mRNA containing a 2'-O-methylpurine cap).

This enzyme belongs to the family of transferases, specifically those transferring one-carbon group methyltransferases. The systematic name of this enzyme class is S-adenosyl-L-methionine:mRNA (nucleoside-2'-O-)-methyltransferase. Other names in common use include messenger ribonucleate nucleoside 2'-methyltransferase, and messenger RNA (nucleoside-2'-)-methyltransferase.

As of late 2007, two structures have been solved for this class of enzymes, with PDB accession codes 2GA9 and 2GAF.

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