The carboxyl terminus of Brca2 links the disassembly of Rad51 complexes to mitotic entry.
The carboxyl terminus of Brca2 links the disassembly of Rad51 complexes to mitotic entry.
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DOI：
10.1016/j.cub.2009.05.057
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发表时间：
2009-07-14
期刊：
影响因子：
--
通讯作者：
Venkitaraman AR
中科院分区：
文献类型：
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作者：
Ayoub N;Rajendra E;Su X;Jeyasekharan AD;Mahen R;Venkitaraman AR
RAD51重组酶组装在DNA上进行同源DNA重组(HR)。这一过程在细胞进入有丝分裂之前修复与复制相关的基因组损伤是必不可少的，但它在细胞周期中如何启动和停止仍然知之甚少。RAD51组装由乳腺癌抑制基因BRCA2通过其进化保守的BRC重复序列和一个独特的羧基(C)末端基序调控，其生物学功能尚不确定。利用“打了就跑”的基因靶向将单密码子替换插入到禽类BRCA2基因座中，我们在这里报告了C-末端基序以前未被认识到的作用。我们发现鸟类的C-末端基序在功能上与人类的C-末端基序同源，并发现了取消或增强RAD51结合的点突变。当这些突变被引入BRCA2中时，我们发现它们既不影响RAD51组装到DNA损伤的核焦点，也不影响HR对DNA的修复。相反，在未能与RAD51结合的点突变中，焦点分解得更快，这与更快的有丝分裂进入有关。相反，在结构性结合RAD51的点突变中，焦点的较慢分解与延迟的有丝分裂相关。事实上，RAD51焦点即使在G2检查点抑制后也不能在有丝分裂细胞中持续存在，这表明它们的分解是染色体分离的先决条件。我们得出结论，C端BRCA2基序的RAD51结合对于HR的执行是必不可少的，而是将RAD51复合体的分解与有丝分裂的进入联系在一起。这一机制可以确保HR在染色体分离之前终止。我们的发现为C末端BRCA2基序指定了一种生物学功能，即在一种机制中协调DNA修复与细胞周期。
The Rad51 recombinase assembles on DNA to execute homologous DNA recombination (HR). This process is essential to repair replication-associated genomic lesions before cells enter mitosis, but how it is started and stopped during the cell cycle remains poorly understood. Rad51 assembly is regulated by the breast cancer suppressor Brca2, via its evolutionarily conserved BRC repeats, and a distinct carboxy (C)-terminal motif whose biological function is uncertain. Using “hit-and-run” gene targeting to insert single-codon substitutions into the avian Brca2 locus, we report here a previously unrecognized role for the C-terminal motif. We show that the avian C-terminal motif is functionally cognate with its human counterpart and identify point mutations that either abolish or enhance Rad51 binding. When these mutations are introduced into Brca2, we find that they affect neither the assembly of Rad51 into nuclear foci on damaged DNA nor DNA repair by HR. Instead, foci disassemble more rapidly in a point mutant that fails to bind Rad51, associated with faster mitotic entry. Conversely, the slower disassembly of foci in a point mutant that constitutively binds Rad51 correlates with delayed mitosis. Indeed, Rad51 foci do not persist in mitotic cells even after G2 checkpoint suppression, suggesting that their disassembly is a prerequisite for chromosome segregation. We conclude that Rad51 binding by the C-terminal Brca2 motif is dispensable for the execution of HR but instead links the disassembly of Rad51 complexes to mitotic entry. This mechanism may ensure that HR terminates before chromosome segregation. Our findings assign a biological function for the C-terminal Brca2 motif in a mechanism that coordinates DNA repair with the cell cycle.