Bishop D K, Williamson M S, Fogel S, Kolodner R D
Nature. 1987;328(6128):362-4. doi: 10.1038/328362a0.
Two different models have been proposed to explain the relative frequencies of the non-mendelian allelic segregations which are detected by tetrad analysis after meiosis in fungi. The first model maintains that 6:2 type tetrads result from correction of heteroduplexes containing mismatched sites and 5:3 type tetrads result from failure to correct mismatched sites. The second model suggests that 6:2 segregations result from the filling-in of double-strand gaps using information obtained from both strands of a homologous duplex. In this model 5:3 type tetrads result if the allele is included in the heteroduplex regions flanking the gap and the resulting mismatched nucleotides are not corrected. We have studied the correction of heteroduplex plasmid DNA in pms1 mutant strains of Saccharomyces cerevisiae, which are known to exhibit higher frequencies of 5:3 type tetrads and lower frequencies of 6:2 tetrads than wild-type strains. Our results suggest that the pms1 mutation causes a defect in mismatch correction, supporting the hypothesis that meiotic gene conversion in wild-type yeast cells often results from the correction of heteroduplex DNA.
为了解释真菌减数分裂后通过四分子分析检测到的非孟德尔等位基因分离的相对频率，已经提出了两种不同的模型。第一个模型认为，6:2型四分子是由含有错配位点的异源双链体的校正产生的，而5:3型四分子是由错配位点未能校正产生的。第二个模型表明，6:2分离是通过使用从同源双链体的两条链获得的信息填充双链间隙而产生的。在这个模型中，如果等位基因包含在间隙两侧的异源双链区域中，并且由此产生的错配核苷酸没有得到校正，就会产生5:3型四分子。我们研究了酿酒酵母pms1突变株中异源双链体质粒DNA的校正情况，已知该突变株比野生型菌株表现出更高频率的5:3型四分子和更低频率的6:2四分子。我们的结果表明，pms1突变导致错配校正缺陷，支持了野生型酵母细胞减数分裂基因转换通常由异源双链DNA校正产生的假设。
