Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America.
School of Biology, Indian Institute of Science Education and Research Thiruvananthapuram, Trivandrum, India.
PLoS Biol. 2023 Apr 20;21(4):e3002085. doi: 10.1371/journal.pbio.3002085. eCollection 2023 Apr.
In most sexually reproducing organisms crossing over between chromosome homologs during meiosis is essential to produce haploid gametes. Most crossovers that form in meiosis in budding yeast result from the biased resolution of double Holliday junction (dHJ) intermediates. This dHJ resolution step involves the actions of Rad2/XPG family nuclease Exo1 and the Mlh1-Mlh3 mismatch repair endonuclease. Here, we provide genetic evidence in baker's yeast that Exo1 promotes meiotic crossing over by protecting DNA nicks from ligation. We found that structural elements in Exo1 that interact with DNA, such as those required for the bending of DNA during nick/flap recognition, are critical for its role in crossing over. Consistent with these observations, meiotic expression of the Rad2/XPG family member Rad27 partially rescued the crossover defect in exo1 null mutants, and meiotic overexpression of Cdc9 ligase reduced the crossover levels of exo1 DNA-binding mutants to levels that approached the exo1 null. In addition, our work identified a role for Exo1 in crossover interference. Together, these studies provide experimental evidence for Exo1-protected nicks being critical for the formation of meiotic crossovers and their distribution.
在大多数有性繁殖的生物体中，减数分裂过程中同源染色体之间的交叉互换对于产生单倍体配子至关重要。在出芽酵母减数分裂中形成的大多数交叉互换都源于双链 Holliday junction (dHJ) 中间体的偏向性解决。这个 dHJ 解决步骤涉及 Rad2/XPG 家族核酸内切酶 Exo1 和 Mlh1-Mlh3 错配修复内切酶的作用。在这里，我们在酿酒酵母中提供了遗传证据，证明 Exo1 通过防止 DNA 切口的连接来促进减数分裂交叉互换。我们发现，Exo1 与 DNA 相互作用的结构元件，如在切口/瓣识别过程中弯曲 DNA 所需的元件，对于其在交叉互换中的作用至关重要。这些观察结果一致表明，Rad2/XPG 家族成员 Rad27 的减数分裂表达部分挽救了 exo1 缺失突变体的交叉缺失缺陷，而 Cdc9 连接酶的减数分裂过表达将 exo1 DNA 结合突变体的交叉水平降低到接近 exo1 缺失的水平。此外，我们的工作确定了 Exo1 在交叉干扰中的作用。总之，这些研究为 Exo1 保护的切口对于减数分裂交叉互换的形成及其分布至关重要提供了实验证据。
