Small nucleolar RNA
class of small RNA molecules that guide chemical modifications of other RNAs
Small nucleolar RNAs (snoRNAs) are a class of non-coding small RNA molecules in the nucleolus that primarily guide chemical modifications of other RNAs, mainly ribosomal RNAs, transfer RNAs and small nuclear RNAs. There are two main classes of snoRNA, the C/D box snoRNAs, which are associated with methylation, and the H/ACA box snoRNAs, which are associated with pseudouridylation.
SnoRNAs are commonly referred to as guide RNAs but should not be confused with the guide RNAs that direct RNA editing in trypanosomes or the guide RNAs (gRNAs) used by Cas9 for CRISPR gene editing.
snoRNA guided modifications
After transcription, nascent rRNA molecules (termed pre-rRNA) undergo a series of processing steps to generate the mature rRNA molecule. Prior to cleavage by exo- and endonucleases, the pre-rRNA undergoes a complex pattern of nucleoside modifications. These include methylations and pseudouridylations, guided by snoRNAs.
Methylation is the attachment or substitution of a methyl group onto various substrates. The rRNA of humans contain approximately 115 methyl group modifications. The majority of these are 2′O-ribose-methylations (where the methyl group is attached to the ribose group).
Pseudouridylation is the conversion (isomerisation) of the nucleoside uridine to a different isomeric form pseudouridine (Ψ).
The public source identifies “Small nucleolar RNA” as class of small RNA molecules that guide chemical modifications of other RNAs. This brief keeps that definition visible, then builds a research path around Small, nucleolar and class.
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This entry incorporates text from “Small nucleolar RNA” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.