preferred_name: a 5'-end (5'-triphosphoguanosine)-(2'-O-methyladenylyl)-adenylyl-cytidylyl-adenosine in mRNA + S-adenosyl-L-methionine => a 5'-end (N(7)-methyl 5'-triphosphoguanosine)-(2'-O-methyladenylyl)-adenylyl-cytidylyl-adenosine in mRNA + S-adenosyl-L-homocysteine