Holliday junction（HJ）是所有生物体在同源重组和DNA损伤修复过程中两条同源DNA相互交叉而产生的一种十字叉状DNA中间体。在修复完成后，HJ必须在HJ解离酶的作用下解离，否则会导致基因组的不稳定性。Moc1是刚被发现的第一个叶绿体特异的HJ解离酶，是确保叶绿体基因组稳定遗传以及叶绿体拟核正确分离的关键。然而，关于Moc1如何特异地识别并剪切底物HJ-DNA的结构机理及其在体内的调控机制均不清楚。本项目拟解析Moc1及其与HJ-DNA底物在多种条件下的复合物晶体结构，包括野生型和突变体Moc1、特异性与非特异性HJ-DNA以及不同金属离子等。我们还将研究Moc1的内源性互作蛋白，探索其在体内可能的作用机制。本项目的完成不仅对全面了解Moc1的分子作用机制以及叶绿体拟核分离的调控机理具有重要的意义，而且对于DNA重组和损伤修复过程也将提供新的认识。

The Holliday junction (HJ) is a key intermediate in homologous recombination and DNA double-strand break repairs for all forms of life. Timely resolution of the junction mediated by HJ resolvases is a fundamental process to maintain genome stability. As a crucial enzyme for chloroplast nucleoid segregation, the monokaryotic chloroplast 1 (Moc1) specifically cleaves four-way HJs in a sequence-dependent manner. However, the molecular mechanisms by which Moc1 specifically recognizes and cleaves its HJ-DNA substrate, either in vitro or in vivo, remained elusive. Here, we propose to determine the structures of Moc1 alone, and in complex with its substrate under various conditions, including wild-type and mutant Moc1, different HJ-DNAs and metal-ions. With the knowledge from these structural studies, we will explore the endogenous molecules interplaying with Moc1 to elucidate its regulatory mechanism in the cells. The success of this work will provide molecular basis for the substrate recognition and cleavage by Moc1, and the basis for chloroplast nucleoid segregation. Given the central role of HJ resolvases in biology, this work is significant to further understand the processes of homologous recombination and DNA double-strand break repairs.