Identification and Cloning of a Yeast Nuclear Gene (CBP1) Involved in Expression of Mitochondrial Cytochrome B

Nuclear pet mutants of Saccharomyces cerevisiae deficient in mitochondrial respiration have been studied genetically and biochemically. Seven noncomplementing mutations leading to a deficiency of mitochondrial cytochrome b have been assigned to a single complementation group (group 60). Examination of mitochondrial RNA by blot hybridization on diazobenzyloxymethyl-paper has revealed that group 60 mutants produce a large number of novel apocytochrome b transcripts not detected in wild-type yeast. The product of the gene affected in the mutants, therefore, appears to be required either for correct transcription or for processing of apocytochrome b premessenger RNA. The gene has been designated CBP1. A representative mutant from complementation group 60 (N5-26) has been transformed to respiratory competency with a recombinant plasmid pool consisting of random fragments of wild-type yeast nuclear DNA inserted into a vector capable of replicating in yeast and Escherichia coli. The complementation of the N5-26 mutation has been shown for a number of independent transformants to be due to the presence of plasmid DNA. The plasmid pG60/T10 was further characterized to have a nuclear DNA insert of 6.7 kilobase pairs. This plasmid complements the mutations of all group 60 mutants, thus confirming that it contains the CBP1 gene.