SCHIZOSACCHAROMYCES-POMBE RNASE MRP RNA IS HOMOLOGOUS TO METAZOAN RNASE MRP RNAS AND MAY PROVIDE CLUES TO INTERRELATIONSHIPS BETWEEN RNASE-MRP AND RNASE-P

RNase MRP and RNase P ribonucleoproteins are structurally and function ally similar across a large evolutionary distance. To better character ize possible complex interrelationships between these two enzymes, we have employed the fission yeast Schizosaccharomyces pombe. Unlike Sacc haromyces cerevisiae, S. pombe is believed to harbour only one genetic locus for the RNA component of RNase P and does not contain a known m itochondrially encoded RNase P RNA. We have identified the single nucl ear gene for the RNA component of RNase MRP in S. pombe, mrp-l, by hom ology to vertebrate RNase MRP RNAs. The mrp-l gene encodes an RNA of m aximum mature length 400 nucleotides that shares a high degree of iden tity, in evolutionarily conserved regions, to both vertebrate RNase MR P RNAs and S. pombe RNase P RNA. Disruption of mrp-l in the diploid st rain SP826 and sporulation of tetrads resulted in a 2 dead:2 viable se gregation, consistent with the gene being essential. Lethality is resc ued by a plasmid-borne copy of mrp-l. Partially purified ribonucleopro tein RNase MRP activity correctly and efficiently processed all previo usly characterized heterologous mitochondrial RNA substrates. The comp act mitochondrial genome of S. pombe contains sequence elements with > 50% identity to mammalian D-loop CSBI and CSBII elements. The identifi cation of mrp-l in S. pombe should facilitate not only comparisons bet ween the related ribonucleoproteins RNase MRP and RNase P, but should also provide an opportunity for genetic elucidation of RNase MRP funct ion in a situation reflective of the animal kingdom.