Department of Molecular Biology and Biotechnology, The University of Sheffield, Sheffield S10 2TN, UK.
Nucleic Acids Res. 2010 Jul;38(13):4349-60. doi: 10.1093/nar/gkq137. Epub 2010 Mar 11.
During meiosis there is an imperative to create sufficient crossovers for homologue segregation. This can be achieved during repair of programmed DNA double-strand breaks (DSBs), which are biased towards using a homologue rather than sister chromatid as a repair template. Various proteins contribute to this bias, one of which is a meiosis specific kinase Mek1. It has been proposed that Mek1 establishes the bias by creating a barrier to sister chromatid repair, as distinct from enforcing strand invasion with the homologue. We looked for evidence that Mek1 positively stimulates strand invasion of the homologue. This was done by analysing repair of DSBs induced by the VMA1-derived endonuclease (VDE) and flanked by directly repeated sequences that can be used for intrachromatid single-strand annealing (SSA). SSA competes with interhomologue strand invasion significantly more successfully when Mek1 function is lost. We suggest the increase in intrachromosomal SSA reflects an opportunistic default repair pathway due to loss of a MEK1 stimulated bias for strand invasion of the homologous chromosome. Making use of an inhibitor sensitive mek1-as1 allele, we found that Mek1 function influences the repair pathway throughout the first4-5 h of meiosis. Perhaps reflecting a particular need to create bias for successful interhomologue events before chromosome pairing is complete.
在减数分裂过程中，必须产生足够的交叉以实现同源体分离。这可以通过修复程序性 DNA 双链断裂（DSB）来实现，修复过程偏向于使用同源体而不是姐妹染色单体作为修复模板。多种蛋白质有助于实现这种偏向性，其中一种是减数分裂特异性激酶 Mek1。有人提出，Mek1 通过在姐妹染色单体修复上创建一个障碍来建立偏向性，而不是用同源体强制进行链入侵。我们寻找证据表明 Mek1 能积极刺激同源体的链入侵。这是通过分析由 VMA1 衍生的内切酶（VDE）诱导的 DSB 的修复来完成的，该酶由可用于染色体内单链退火（SSA）的直接重复序列侧翼。当 Mek1 功能丧失时，SSA 与同源体链入侵之间的竞争显著更加成功。我们认为，由于 Mek1 刺激的同源染色体链入侵偏向性丧失，染色体内 SSA 的增加反映了一种机会主义的默认修复途径。利用对抑制剂敏感的 mek1-as1 等位基因，我们发现 Mek1 功能会影响整个减数分裂前 4-5 小时的修复途径。这可能反映出在染色体配对完成之前，特别需要为成功的同源体事件建立偏向性的需求。
