MATING-TYPE DIFFERENTIATION BY TRANSPOSITION OF CONTROLLING ELEMENTS IN SACCHAROMYCES CEREVISIAE

[摘要] The nonfunctional mutation of the homothallic gene HMLα , designated hmlα , produced two mutant alleles, hmlα -1 and hmlα -2. Both mutant clones were mixed cultures consisting of a mating-type cells and nonmating haploid cells. The frequencies of the two cell types were different, and a few diploid cells able to sporulate were found in the hmlα -2 mutant. Conversions of an a mating-type cell to nonmater, and uice uersa , were observed in both mutants. The conversion of an a mating phenotype to nonmating is postulated to occur by alteration of the a mating type to the sterile mating-type allele in the hmlα -1 mutant. In tetrad dissection of prototrophic diploids that were obtained by rare-mating of hmlα -1 mutants with a heterothallic strain having the MATa ho HMRa HMLa genotype, many mating-deficient haploid segregants were found, while α mating-type segregants were observed in a similar diploid using an hmlα-2 mutant. The mating-type-deficient haploid segregants were supposed to have the sterile a mating-type allele because the nonmating genetic trait always segregated with the mating-type locus. Sporogenous diploid cells obtained in the hmlα -2 mutant clone had the MATa/MAT,α HO/HO HMRa/ HMRa hmlα-2/hmlα-2 genotype . These observations suggested that the hmla-I allele produces a transposable element that gives rise to the sterile su mating type by transposition into the mating-type locus, and that the hmlα -2 allele produces an element that provides,α mating-type information, but is defective in the structure for transposition.

[学科分类] 医学（综合）