Cap-specific mRNA (nucleoside-2'-O-)-methyltransferase 1 (CMTR1)

S-adenosyl-L-methionine-dependent methyltransferase that mediates mRNA cap1 two'-O-ribose methylation into the 5'-cap structure of mRNAs. Methylates the ribose of the first nucleotide of a m(7)GpppG-capped mRNA and small nuclear RNA (snRNA) to produce m(7)GpppRm (cap1).

Displays a preference for cap0 transcripts. Cap1 modification is connected to high levels of translation.