Fragments of small nucleolar RNAs as a new source for noncoding Rnas

Small nucleolar RNAs (snoRNAs) are small, nonprotein-coding RNAs that accumulate in the nucleolus. So far, these RNAs have been implicated in modification of rRNAs, tRNAs, and snRNAs. snoRNAs can be grouped into two classes: C/D box and H/ACA box snoRNAs that direct 2′-O-methylation and pseudouridylation, respectively. However, for numerous snoRNAs, no target RNAs have been identified. High-throughput sequencing and detailed analysis of RNase protection experiments have demonstrated that some snoRNAs are processed into smaller RNAs. These processed snoRNAs are 20-100 nt in length, are mostly nuclear and do not form canonical snoRNPs, that is, they do not associate with methylase or pseudouridylation activity. They can act by binding to pre-mRNAs in the nucleus where they regulate alternative pre-mRNA splicing. Thus, processed snoRNAs (psnoRNAs) represent a novel class of regulatory RNAs.