SITE-SPECIFIC RIBOSE METHYLATION OF PRERIBOSOMAL RNA - A NOVEL FUNCTION FOR SMALL NUCLEOLAR RNAS

Eukaryotic cells contain many fibrillarin-associated small nucleolar R NAs (snoRNAs) that possess long complementarities to mature rRNAs. Cha racterization of 21 novel antisense snoRNAs from human cells followed by genetic depletion and reconstitution studies on yeast U24 snoRNA pr ovides evidence that this class of snoRNAs is required for site-specif ic 2'-O-methylation of preribosomal RNA (pre-rRNA). Antisense snoRNAs function through direct base-pairing interactions with pre-rRNA. The a ntisense element, together with the D or D' box of the snoRNA, provide the information necessary to select the target nucleotide for the met hyltransfer reaction. The conclusion that snoRNAs function in covalent modification of the sugar moieties of ribonucleotides demonstrates th at eukaryotic small nuclear RNAs have a more versatile cellular functi on than earlier anticipated.