期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1980
卷号：77
期号：5
页码：2824-2828
DOI：10.1073/pnas.77.5.2824
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Homothallic strains of Saccharomyces cerevisiae can switch from one mating type to the other as often as every cell division. The conversion of mating type alleles (from MATa to MAT or vice versa) depends on other, unexpressed copies of a or information that can be transposed to MAT. Previously, "inconvertible" mutations within MAT and MATa have been described that block the excision of the MAT allele. In this paper we describe two cis-acting mutations that also impair mating type switching and lie very near, but outside, the MAT locus. Both "stuck" mutations, stk1 and stk2, diminish the efficiency of converting MATa to MAT to less than 10% of normal. The stk1 mutation also slightly reduces conversion of MAT to MATa, whereas stk2 has no discernible effect. Unlike the inconvertible MAT-inc and MATa-inc mutations within MAT, the stk mutations are not replaced by wild-type sequences after the "stuck" cells occasionally switch to the opposite mating type. Because these mutations are not "healed" by mating type conversions, they must lie in sequences outside of the transposable mating type information. These results indicate that the efficient replacement of MAT alleles depends on sequences both within and adjacent to the MAT locus. Among subclones of homothallic stk MATa strains, approximately 2% show "illegal" transpositions of mating type genes. In these colonies the silent copy of information at the HML locus has been converted to a, without any change of MATa or the silent a copy at HMRa. Such conversions of the unexpressed library genes are not found in wild-type homothallic strains that can switch mating type efficiently, but they are found in MATa-inc and MAT-inc strains. It appears that all of the cis-acting mutations within or adjacent to mating type result in these unusual switches of mating type information at HML and HMR.
关键词：homothallism ; yeast mating type conversion ; Saccharomyces cerevisiae
