Fig. 4. C/D box snoRNPs modifie the target RNA by 2′-O-methylation.

SnoRNAs bind to target RNAs by antisense elements upstream of D box and/or D’ box. SnoRNAs form functional snoRNPs by binding to four core proteins, including Nop1p, Nop56p, Nop58p, and Snu13p. Among them, Nop1p transfers the methyl group on s-adenosine-methionine to the 2′- hydroxyl group of the target RNA ribose.