Notes: N4-Acetyl-2'-O-methylcytidine (ac4Cm) is a pyrimidine nucleoside and a post-transcriptionally modified derivative of cytidine (Item No. 29602).{67635} ac4Cm has been found in the tRNA and 5S rRNA of Archaea thermophiles and increases RNA rigidity and stability through stronger complimentary base pairing with the purine nucleoside guanosine (Item No. 27702) compared to cytidine.{67635,67636}