COMPARATIVE STRUCTURAL-ANALYSIS OF NUCLEAR RNASE-P RNAS FROM YEAST

Secondary structure models for yeast nuclear RNase P RNAs were derived by phylogenetic comparative analysis. RNase P RNA genes from six Sacc haromyces species were characterized and compared with the published g ene sequences of Saccharomyces cerevisiae (RPR1), Schizosaccharomyces pombe, and Schizosaccharomyces octosporus. The general organization of the Saccharomyces genes were similar: all were present in single copy and contained RNA polymerase III-specific regulatory elements, includ ing tRNA gene-like A- and B-box promoters located within 5' leader reg ions and poly(T) terminators following the mature RNA domain. As obser ved previously, two RNase P RNAs were present in each of the species: a shorter RNA corresponding to the mature domain and a longer possible precursor RNA that includes the 5' leader sequences. The mature RNA d omains of three of these genes were sufficiently divergent from the S. cerevisiae RNA such that compensatory base changes in paired elements were readily identified, yet homologous regions could be aligned. A s triking common core of primary and secondary structure emerged for the Saccharomyces RNase P RNAs. Furthermore, the Schizosaccharomyces homo logs conformed in large part to the Saccharomyces conserved core and s hared with it a distinctive structural domain that has so far only bee n observed in the yeast nuclear RNase P RNAs. Comparison of the yeast core to a previously published eubacterial conserved core and to the R NA homologs from vertebrates revealed a number of similarities, sugges ting that RNase P RNA from diverse sources may share a core of structu rally conserved elements.