Non-coding RNAs: lessons from the small nuclear and small nucleolar RNAs

We now understand that genomes in all three domains of life produce functional RNAs that do not encode proteins (non-coding (nc)RNAs), but do exert important influences on diverse cellular processes.Most ncRNAs function with essential partner proteins (that is, as non-coding ribonucleoproteins; ncRNPs) and use cognate antisense elements to interact with target molecules. The small nuclear (sn)RNAs and small nucleolar (sno)RNAs are founding members of the family of ncRNAs that helped to establish these common paradigms.Recent studies of the snRNPs and snoRNPs have revealed unexpectedly elaborate biogenesis pathways that will probably also be travelled by other ncRNPs.snRNAs and snoRNAs can be transcribed from independent promoters (similar to mRNAs) or can be encoded within intronic sequences.RNA function can require multiple partner proteins with roles that might include modulating RNA structure or securing an enzyme, as well as catalysing the reaction.Assembling a functional complex seems to involve a series of non-functional intermediate states that are matured by a series of cellular factors along a defined physical pathway in the cell. These transport and assembly steps might serve as control points for the regulation of the activity of a given ncRNP.