Comparative sequence analysis as an approach to evaluating structure, function, and evolution of 5S and 5.8S ribosomal RNAs.

Nucleotide sequences of nine eukaryotic and nine eubacterial 5S rRNAs have been selected for their diversity and subjected to analysis of primary and potential secondary structure. This analysis has allowed the quantitative confirmation of several previously made observations concerning 5S rRNA structure: (i) these two 5S rRNAs are derived from a common ancestor and probably perform essentially the same function in protein synthesis; (ii) one domain of 5S rRNA has undergone considerable divergence of structure (and presumably function) since the separation of the eukaryotic and eubacterial lineages; and (iii) single-stranded regions are more highly conserved than double-stranded regions. In addition, this analysis leads us to propose that (i) some of the highly conserved nucleotide residues in single-stranded regions interact in a specific manner with protein components of the translational apparatus, and (ii) repetitive folding and unfolding of helical regions occurs in two regions of eukaryotic 5S rRNA and one region of eubacterial 5S rRNA. In the context of these observations and propositions we also consider the potential secondary structure of plant mitochondrial 5S rRNA. Nucleotide sequences of 5.85 rRNAs have yielded less information about secondary structure and possible functional interactions. However, we have identified highly conserved and variable regions within this molecule and we show (in contrast to the situation with 5S rRNA) that these do not correlate well with proposed single-stranded and helical regions in a current model of 5.8S secondary structure.