RPM2 is a Saccharomyces cerevisiae nuclear gene required for normal cell growth yet the only known function of Rpm2p is as a protein subunit of yeast mitochondrial RNase P, an enzyme responsible for the 5' maturation of mitochondrial tRNAs. Since mitochondrial protein synthesis in S. cerevisiae is not essential for viability, RPM2 must provide another function in addition to its known role as a mitochondrial tRNA processing enzyme. During a search for RPM2 homologues from Kluyveromyces lactis, we recovered a K. lactis gene that compensates for the essential function but not the RNase P function of RPM2. We have named this gene SEF1 (Suppressor of the Essential Function), DNA sequence analysis of SEF1 reveals it contains a Zn(2)-Cys(6) binuclear cluster motif found in a growing number of yeast transcription factors. The SEF1 homologue of S. cerevisiae also compensates for the essential function of RPM2. The two proteins share 49% identity and 72% amino acid sequence similarity.