Identification of amino acid substitutions in the dicyclohexylcarbodiimide-binding subunit of the mitochondrial ATPase complex from oligomycin-resistant mutants of Saccharomyces cerevisiae.

1. Oligomycin-resistant mutants of Saccharomyces cerevisiae strain D273-10B/A1 have been assigned to three previously defined mitochondrial genetic loci, olil, oli2 and oli3. Standard crosses of o/iJ-resistant mutants yielded a low percentage of sensitive recombinants indicating that the mutations were in closely linked but separate alleles. 2. The oligomycin-resistant mutants were used to study the amino acid sequence of the dicyclohexylcarbodiimide-binding subunit of the mitochondrial ATPase complex. Two different amino acid substitutions have been identified in the dicyclohexylcarbodiimide-binding protein of a/ilresistant mutants: leucine/phenylalanine at residue 53 or cysteinejserine at residue 65. The protein of the single o/i3-resistant strain examined had a leucinejvaline exchange in residue 57. No differences were noted in the dicyclohexylcarbodiimide-binding protein of the oli2-resistant mutant when the amino acid composition of cyanogenbromide fragments as well as a partial sequence were compared with the wild type. These data indicate that the olil and o/i3locus are in the structural gene of the dicyclohexylcarbodiimide-binding protein and they suggest that the oli2 locus is in some other still unidentified mitochondrial gene. 3. Aminoacid sequence data have also been obtained for the dicyclohexylcarbodiimide-binding protein of a revertant of an A TPase-deficient pho2 mutant. The protein of the revertant strain was ascertained to have a serinefleucine exchange at residue 42. The localization of the pho2 locus in the structural gene of the dicyclohexylcarbodiimide-binding protein is in agreement with previous evidence that mutations in the pho2 and olil loci are genetically linked. 4. The frequencies of recombination among the olil and oli3 resistant mutants have been related to the distances of the amino acids affected by the mutations. lt is concluded that mutations in adjacent amino acids recombine with a frequency of 0.01 %.