Klar A J
Genetics. 1980 Jul;95(3):631-48. doi: 10.1093/genetics/95.3.631.
The a and alpha cell types of budding yeast saccharomyces cerevisiae are controlled by alternate alleles of the mating-type locus (MAT), MATa and mat alpha. The cell types can be interconverted by switching alleles of MAT. The loci HMRa and HML alpha, which are loosely linked to MAT, are involved in mating-type switching. Experimental evidence for their role in MAT interconversion is presented. As a result of switching, the homothallic and heterothallic strains containing the amber and ochre mutations within the HMRa locus yield corresponding amber and ochre mutant mata loci. Similarly, the hml alpha mutant strain generates mat alpha mutant alleles. That is, specific mutations from HMRa and HML alpha are transmitted to MAT. A replica of the mating-type coding information originating from these loci is transposed to MAT, where it replaces the existing information. Furthermore, "Hawthorne deletions" in strains containing hmra-amber/ochre result in production of mata-amber/ochre alleles. Therefore, genetic information for MATa resides at HMRa. The switches occur in a defined set of clonally related cells. Thus, the efficient interconversion of yeast cell types is mediated by an unidirectional transfer of genetic information between nonallelic sites in a nonrandom and programmed fashion. The results are inconsistent with the "flip-flop" models, but satisfy a key prediction of the general controlling element and the specific cassette models proposed for mating-type interchange.
出芽酵母酿酒酵母的a细胞类型和α细胞类型由交配型基因座（MAT）的等位基因MATa和matα控制。细胞类型可通过转换MAT的等位基因来相互转变。与MAT松散连锁的基因座HMRa和HMLα参与交配型转换。文中给出了它们在MAT相互转变中作用的实验证据。由于转换的结果，在HMRa基因座内含有琥珀突变和赭石突变的同宗配合和异宗配合菌株产生了相应的琥珀突变和赭石突变的mata基因座。同样，hmlα突变菌株产生matα突变等位基因。也就是说，来自HMRa和HMLα的特定突变被传递到MAT。源自这些基因座的交配型编码信息的一个副本被转座到MAT，在那里它取代了现有的信息。此外，含有hmra - 琥珀/赭石的菌株中的“霍桑缺失”导致mata - 琥珀/赭石等位基因的产生。因此，MATa的遗传信息位于HMRa。转换发生在一组特定的克隆相关细胞中。因此，酵母细胞类型的有效相互转变是由遗传信息在非等位基因位点之间以非随机和程序化的方式进行单向转移介导的。这些结果与“触发器”模型不一致，但符合为交配型互换提出的一般控制元件模型和特定盒式模型的一个关键预测。
