The organization and regulation of expression of the yeast mitochondrial genome will be studied. Particular emphasis will be placed on a novel mitochondrial gene recently discovered in our laboratory, termed var 1. Two major lines of investigation are considered: a) isolation, characterization, and determination of the function of the var 1 protein product and b) identification, isolation, and characterization of var 1 mRNA. These studies are directed, in part, to an analysis of the regulation of expression of the var 1 gene. They will be extended to a general characterization of the major transcripts of the yeast mitochondrial DNA and their assignment to defined segments of the wild-type genome. In all of these studies, extensive use will be made of our large collection of wild-type, petite and mit- strains whose mitochondrial genomes have been well characterized genetically and physically by restriction endonuclease analysis. Finally, we propose to extend the application of a procedure developed in our laboratory termed zygotic gene rescue to a) the analysis of "complex" mitochondrial genes, and in particular, the region of the genome encoding the cytochrome b apoprotein and b) a determination of cis versus trans regulatory interactions in heteroplasmic configurations of mitochondrial DNA molecules.