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