Mitochondrial cytochrome b genes with a six-nucleotide deletion or single-nucleotide substitutions confer resistance to antimycin A in the yeast Kluyveromyces lactis.

Extrachromosomal mutants resistant to antimycin, from the yeast Kluyveromyces lactis, have been isolated, genetically characterized, and assigned to two specific genetic loci (Brunner et al., 1987). In the present work the cytochrome b nucleotide sequence from six of these mutants was determined. Five mutants had single point mutations, corresponding to transversions. In one mutant, a six-base-pair deletion, beginning at nucleotide 689, was observed. The amino acid sequence derived from the coding strand showed that, in three independent antimycin-resistant mutants, a change of asparagine 31 into lysine took place (two of these mutants are also resistant to diuron). Two other mutants showed a change from lysine 228 into isoleucine (or methionine). Leucine 230, isoleucine 231, and threonine 232, were lost in the deletion mutant and were replaced by serine.