A guided tour: small RNA function in Archaea

In eukaryotes, the C/D box family of small nucleolar (sno)RNAs contain comp lementary guide regions that are used to direct 2'-O-ribose methylation to specific nucleotide positions within rRNA during the early stages of riboso me biogenesis. Direct cDNA cloning and computational genome searches have r evealed homologues of C/D box snoRNAs (called sRNAs) in prokaryotic Archaea that grow at high temperature. The guide sequences within the sRNAs indica te that they are used to direct methylation to nucleotides in both rRNAs an d tRNAs. The number of sRNA genes that are detectable within currently sequ enced genomes correlates with the optimal growth temperature. We suggest th at archaeal sRNAs may have two functions: to guide the deposition of methyl groups at the 2'-O position of ribose, which is an important determinant i n RNA structural stability, and to serve as a molecular chaperones to help orchestrate the folding of rRNAs and tRNAs at high temperature.