preferred_name: a 5'-end (N(2),N(7)-dimethyl 5'-triphosphoguanosine)-ribonucleoside in snoRNA + S-adenosyl-L-homocysteine + H(+) => a 5'-end (N(7)-methyl 5'-triphosphoguanosine)-ribonucleoside in snoRNA + S-adenosyl-L-methionine