The nucleolar snRNAs: catching up with the spliceosomal snRNAs.

Despite their early discovery, research into the small RNAs associated with the eukaryotic nucleolus (snoRNAs) has lagged behind that of their cousins, the small nuclear RNAs which are known to function in mRNA splicing (spliceosomal snRNAs). Recent progress has now shown that the snoRNAs also occupy a vital niche in the RNA world, participating in the processing of ribosomal RNA. Like the spliceosomal snRNAs, the snoRNAs exist as ribonucleoprotein (RNP) particles which appear to assemble into a large multi-RNA RNP complex for pre-rRNA maturation.