Rpm2p: separate domains promote tRNA and Rpm1r maturation in Saccharomycescerevisiae mitochondria

Rpm2p is a protein subunit of yeast mitochondrial RNase P and is also requi red for the maturation of Rpm1r, the mitochondrially-encoded RNA subunit of the enzyme. Previous work demonstrated that an insertional disruption of R PM2, which produces the C-terminally truncated protein Rpm2-Delta Cp, suppo rts growth on glucose but cells lose some or all of their mitochondrial gen ome and become petite. These petites, even if they retain the RPM1 locus, l ose their ability to process the 5 ' -ends of mitochondrial tRNA. We report here that if strains containing the truncated RPM2 allele are created and maintained on respiratory carbon sources they have wild-type mitochondrial genomes, and a significant portion of tRNA transcripts are processed. In co ntrast, precursor Rpm1r transcripts accumulate and mature Rpm1r is not made . These data show that one function of the deleted C-terminal region is in the maturation of Rpm1r, and that this region and mature Rpm1r are not abso lutely required for RNase P activity. Finally, we demonstrate that full act ivity can be restored if the N-terminal and C-terminal domains of Rpm2p are supplied in trans.