Substitution for some but not all functions of Saccharomyces cerevisiae RPM2 by Candida glabrata RPM2, Kluyveromyces lactis EBS1 and Saccharomyces cerevisiae YDL189W

RPM2 codes for a multifunctional protein, required for one or more unknown functions, as well as for functions necessary to support Saccharomyces cerevisiae mitochondrial RNase P activity. This complex is a ribonucleoprotein that removes the 5′ leader sequence from mitochondrial precursor tRNAs. This processing is a necessary step to create tRNAs that can participate in protein synthesis. Rpm2p is also required for the synthesis of fully processed Rpm1r, the RNA subunit of yeast mitochondrial RNase P. To learn more about Rpm2p, I undertook a screen that took advantage of the observation that cells containing a truncated form of Rpm2p lose their wild-type mitochondrial genomes when grown on glucose media and therefore become respiratory incompetent. Selection for genes that allow these cells to maintain respiratory competency and thus their mitochondrial DNA resulted in the recovery of the Candida glabrata homolog of RPM2 (Cg RPM2). Cells reliant on Cg Rpm2p as their sole source of Rpm2p process mitochondrial tRNA. Thus, Cg Rpm2p and S. cerevisiae Rpm1r can work together to perform tRNA processing as well as promote the maturation of Rpm1r. The protein also supports the unknown function that is necessary for fermentative growth, but it is compromised in a newly identified second respiratory function of Rpm2p. This screen was also used to identify K. lactis EBS1 and S. cerevisiae YDL189W as two genes that suppress the loss of mitochondrial DNA. Their mechanism of action is unknown, but does not involve improvement in RNase P activity caused by truncation of Rpm2 protein.