Identification and Characterization of a Yeast Mitochondrial Locus Necessary for tRNA Biosynthesis

Abstract

It is well established that yeast mtDNA codes for tRNAs used in mitochondrial protein synthesis. Very little is known about the expression of those tRNA genes and the processes necessary to produce functional tRNAs in mitochondria. One approach toward the elucidation of tRNA biosynthetic pathways is to analyze tRNA biosynthesis in mitochondrial mutants. Petite mutants are mtDNA deletion mutants that have lost various portions of the wild-type genome. Some petites that retain tRNA genes make tRNAs indistinguishable from wild-type tRNAs (Martin et al. 1976; Newman et al. 1980), whereas other petites that retain tRNA genes make transcripts from their tRNA genes but do not produce tRNAs (Martin et al. 1976; Martin and Underbrink-Lyon 1981). Since the ability to produce tRNA could be correlated with retention of a particular region of mtDNA, Morimoto et al. (1979) suggested that a mitochondrial locus was necessary for tRNA biosynthesis. We have now demonstrated the presence of such a locus by complementation analysis; we have located it within 2100 bp of the wild-type genome and have characterized it by restriction mapping and DNA sequencing.

COMPLEMENTATION ANALYSIS OF THE tRNA SYNTHESIS LOCUS
If a locus on mtDNA is necessary for tRNA synthesis, then a petite that has the locus should restore the ability to synthesize tRNA to a petite that does not make tRNA from the tRNA genes it retains. A mating procedure that allows two mitochondrial genomes to be maintained in a diploid state (Strausberg and Butow 1978) was used to test this hypothesis. Restoration...