Specificity and origin of the Mod2- mutation which restores respiratory sufficient phenotype in some pet mutants in Saccharomyces cerevisiae.

It has been found that Mod2- mutation restores respiratory sufficient phenotype in cytochrome b less mutant MB127-20C. Mod2- gene when present in the same haploid cell with mutant gene pet25 causing deficiency in cytochromes a+a3 and b seems to be responsible for reappearance of cytochrome b in the cytochrome spectrum as well partial respiratory activity. However, the restored respiratory activity seems to be inefficient as growth on unfermentable carbon sources is still impossible. Evidences are presented that the Mod2- mutation originates from respiratory sufficient strain 18-27 in which op1 mutation has been induced.