Pannafino Gianno, Chen Jun Jie, Mithani Viraj, Payero Lisette, Gioia Michael, Brooks Crickard J, Alani Eric
Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, USA 14853.
bioRxiv. 2023 Nov 13:2023.11.13.566911. doi: 10.1101/2023.11.13.566911.
The accurate segregation of homologous chromosomes during the Meiosis I reductional division in most sexually reproducing eukaryotes requires crossing over between homologs. In baker's yeast approximately 80 percent of meiotic crossovers result from Mlh1-Mlh3 and Exo1 acting to resolve double-Holliday junction (dHJ) intermediates in a biased manner. Little is known about how Mlh1-Mlh3 is recruited to recombination intermediates and whether it interacts with other meiotic factors prior to its role in crossover resolution. We performed a haploinsufficiency screen in baker's yeast to identify novel genetic interactors with Mlh1-Mlh3 using sensitized alleles that disrupt the stability of the Mlh1-Mlh3 complex and confer defects in mismatch repair but do not disrupt meiotic crossing over. We identified several genetic interactions between and the recombinase responsible for recombination between homologous chromosomes during meiosis. We then showed that Mlh3 physically interacts with Dmc1 and at times in meiotic prophase when Dmc1 acts as a recombinase. Interestingly, restricting expression to roughly the time of crossover resolution resulted in a null-like phenotype for crossing over. Our data are consistent with a model in which Dmc1 nucleates a polymer of Mlh1-Mlh3 to promote crossing over.
在大多数有性生殖的真核生物减数分裂I减数分裂过程中，同源染色体的准确分离需要同源染色体之间发生交叉互换。在酿酒酵母中，大约80%的减数分裂交叉互换是由Mlh1-Mlh3和Exo1以一种有偏向性的方式作用于解决双Holliday连接（dHJ）中间体而产生的。关于Mlh1-Mlh3如何被招募到重组中间体以及在其参与交叉互换解决作用之前是否与其他减数分裂因子相互作用，我们了解得很少。我们在酿酒酵母中进行了单倍体不足筛选，使用破坏Mlh1-Mlh3复合物稳定性并导致错配修复缺陷但不破坏减数分裂交叉互换的敏感等位基因，来鉴定与Mlh1-Mlh3的新型遗传相互作用因子。我们确定了减数分裂过程中负责同源染色体间重组的重组酶与Mlh1-Mlh3之间的几种遗传相互作用。然后我们表明，Mlh3在减数分裂前期有时会与Dmc1发生物理相互作用，此时Dmc1作为一种重组酶。有趣的是，将Dmc1的表达限制在大致交叉互换解决的时间会导致交叉互换出现类似无效的表型。我们的数据与一个模型一致，即Dmc1使Mlh1-Mlh3聚合物成核以促进交叉互换。
