5′ processing of Saccharomyces cerevisiae mitochondrial tRNAs requires expression of multiple genes

Mitochondrial tRNAs are processed at their 5'ends by highly divergent but ubiquitous RNase P. In Saccharomyces cerevisiae, Rpm2p is the protein component of RNase P. Here, we identify four novel genes MTA1, MTA2, GEP5 and PET130 of the Saccharomycetaceae family that are necessary for an efficient processing of mitochondrial tRNAs. Null mutants of mtal, mta2 and gep5 have severely reduced levels of mitochondrial tRNAs; in addition, temperature sensitive (ts) mutants of mtal, mta2, pet130 and gep5 accumulated tRNAs precursor transcripts at the restrictive but not at the permissive temperature. The same mitochondrial tRNAs precursors were also identified in tprn2 ts mutants or in the double ts mutants mtal rpm2 and mta2 rpm2. The genetic and physical association of these four novel genes corroborate the hypothesis that they have their function associated. Different combinations of mtal, mta2, pet130 and gep5 ts alleles display a synthetic respiratory deficient phenotype, an indication of genetic interactions of the genes. Indeed, Mta1p, Mta2p, Pet130p, and Gep5p are associated with the mitochondria] inner membrane and are all extracted and sediment in sucrose gradients as high molecular weight complexes, where they may be present in a common complex with Rpm2p. This is supported by pull-down assays showing co-immunopurification of Rpm2 with Mta1p.