Control of Gene Expression in the Biosynthesis of Mitochondrial Ribosomes

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Eukaryotic cells maintain distinct organellar and cytoplasmic systems of protein synthesis, and there appears to be very overlap between the gene familes that specify the components of the two systems. The genes for components of the organellar translation systems are divided between two genetic systems. For the mitochondrial translation system of Saccharomyces cerevisiae, the rRNAs, tRNAs and one ribosomal protein are specified by the mitochondrial genome, and over 100 additional proteins are encoded by nuclear genes. Combined molecular biological and genetic approach is being taken to identify and characterize nuclear genes in yeast that encode components of the mitochondrial protein synthetic machinery. These genes are being cloned by immunological screening of a yeast genomic library constructed in the gtll phage expression vector and by genetic complementation of temperature-sensitive mutants that are defective in mitochondrial protein synthesis. The cloned genes, combined with specific immunological probes, provide the tools to systematically study the structure, function, and regulation of a unique set of translational components. Studies thus far have been focussed on three genes, each of which appears to be subject to different modes of regulation. Of particular interest are two genes that are regulated posttranscriptionally. A major part of this proposal is devoted to the critical evaluation of the possibility that these genes are subject to unique forms of translational control. How different genomes in the same cell communicate is still a genetic mystery. The results of this study should give greater insight into that process.