Ribose 2'-O-methylation, the most common nucleotide modification in mammalian rRNA, is directed by the C/D box small nucleolar RNAs (snoRNAs). Thus far, more than fifty putative human rRNA methylation guide snoRNAs have been identified. For nine of these snoRNAs, the respective ribose methylations in human 28S rRNA have been only presumptive.
In this study, the methylation state of human 28S rRNA in the positions predicted by the snoRNAs U21, U26, U31, U48, U50, U73, U74, U80 and U81 was assessed using reverse transcription-based methods and several novel 2'-O-methylations were localized.
Seven novel ribose 2'-O-methylated residues (Am389, Am391, Gm1604, Gm1739, Gm2853, Cm3810, Gm4156, predicted by snoRNAs U26, U81, U80, U73, U50, U74 and U31, respectively) have been localized in human 28S rRNA. The total number of 2'-O-methylations in human rRNA is not yet known.