1. 1. A mutant yeast which is incapable of absorbing oxygen was obtained by ultraviolet irradiation. The mutant does not exhibit absorption bands for cytochromes-a and -b and shows a marked reduction in the bands characteristic of cytochrome-c. 2. 2. When this cytochrome-deficient mutant is crossed with petite, another cytochrome-deficient haploid, normal diploids are obtained. The appearance of normal and mutant yeast in a 1:1 ratio indicates that the cytochrome deficiency can be referred to the segregation of a single gene. 3. 3. None of the haploid segregants are petite, but all the clones from normal spores produce some petite colonies when plated. These results can be accounted for if the petites are genetically normal but deficient in a cytoplasmic factor which is also necessary for the production of the complete cytochrome system. 4. 4. A great many reversions to normal were observed among the clones from some mutant segregants. No reversions were found in other mutant segregants. These observations makes questionable the classification of normal and cytochrome deficient segregants by tests that utilize large masses of cells, unless the homogeneity of the population is verified.

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petite normal segregants cytochrome deficiency b cytochromesa cytochromec

Caroline Raut,.A cytochrome deficient mutant of Saccharomyces cerevisiae. 4 (2),295-305.

Caroline Raut,"A cytochrome deficient mutant of Saccharomyces cerevisiae" 4

Caroline Raut,"A cytochrome deficient mutant of Saccharomyces cerevisiae"