Klar A J, Bonaduce M J
NCI-Frederick Cancer Research and Development Center, ABL-Basic Research Program, Laboratory of Eukaryotic Gene Expression, Frederick, Maryland 21702-1201.
Genetics. 1991 Dec;129(4):1033-42. doi: 10.1093/genetics/129.4.1033.
Mitotic interconversion of the mating-type locus (mat1) of the fission yeast Schizosaccharomyces pombe is initiated by a double-strand break at mat1. The mat2 and mat3 loci act as nonrandom donors of genetic information for mat1 switching such that switches occur primarily (or only) to the opposite mat1 allele. Location of the mat1 "hot spot" for transposition should be contrasted with the "cold spot" of meiotic recombination located within the adjoining mat2-mat3 interval. That is, meiotic interchromosomal recombination in mat2, mat3 and the intervening 15-kilobase region does not occur at all. swi2 and swi6 switching-deficient mutants possess the normal level of double-strand break at mat1, yet they fail to switch efficiently. By testing for meiotic recombination in the cold spot, we found the usual lack of recombination in a swi2 mutant but a significant level of recombination in a swi6 mutant. Therefore, the swi6 gene function is required to keep the donor loci inert for interchromosomal recombination. This finding, combined with the additional result that switching primarily occurs intrachromosomally, suggests that the donor loci are made accessible for switching by folding them onto mat1, thus causing the cold spot of recombination.
裂殖酵母粟酒裂殖酵母（Schizosaccharomyces pombe）交配型位点（mat1）的有丝分裂相互转换由mat1处的双链断裂引发。mat2和mat3位点作为mat1转换的遗传信息非随机供体，使得转换主要（或仅）发生到相反的mat1等位基因。mat1转座“热点”的位置应与位于相邻mat2 - mat3区间内的减数分裂重组“冷点”形成对比。也就是说，mat2、mat3及中间15千碱基区域根本不发生减数分裂染色体间重组。swi2和swi6转换缺陷型突变体在mat1处具有正常水平的双链断裂，但它们不能有效地进行转换。通过检测冷点处的减数分裂重组，我们发现在swi2突变体中通常不存在重组，但在swi6突变体中有显著水平的重组。因此，需要swi6基因功能来使供体位点对染色体间重组保持惰性。这一发现，再加上转换主要发生在染色体内的额外结果，表明供体位点通过折叠到mat1上而可用于转换，从而导致重组冷点。
