Su Xinyi, Bernal Juan A, Venkitaraman Ashok R
The Medical Research Council Cancer Cell Unit, Hutchison/MRC Research Centre, Hills Road, Cambridge CB2 0XZ, UK.
Nat Struct Mol Biol. 2008 Oct;15(10):1049-58. doi: 10.1038/nsmb.1490. Epub 2008 Sep 14.
Coordination of homologous DNA recombination (HDR) with DNA replication maintains the fidelity of cell division. Exploiting Varshavsky's N-end rule to create a thermosensitive degron for conditional genetics in an avian cell line, we confirm that inactivation of the essential HDR enzyme Rad51 in a single cell cycle does not stop replicative DNA synthesis but, instead, causes G2 arrest. Rad51 complementation after the completion of replication overcomes this block, suggesting that HDR becomes necessary in G2. Indeed, DNA structures that bind activated replication protein A accumulate during the S phase, to be preferentially resolved during G2 by a Rad51-dependent mechanism. Breaks affecting a single chromatid predominate after the first cell cycle without Rad51, subsequently evolving into isochromatid lesions. We suggest a model for the vertebrate cell cycle in which HDR during the G2 phase is separated from DNA replication in S phase and chromosome segregation in M.
同源DNA重组（HDR）与DNA复制的协调维持了细胞分裂的保真度。利用瓦尔沙夫斯基的N端规则在禽细胞系中创建一个用于条件遗传学的热敏降解子，我们证实，在单个细胞周期中使必需的HDR酶Rad51失活不会停止复制性DNA合成，而是导致G2期停滞。复制完成后Rad51的互补作用克服了这一障碍，表明HDR在G2期变得必要。事实上，与活化的复制蛋白A结合的DNA结构在S期积累，在G2期通过依赖Rad51的机制优先得到解决。在没有Rad51的第一个细胞周期后，影响单个染色单体的断裂占主导，随后演变为等臂染色单体损伤。我们提出了一个脊椎动物细胞周期模型，其中G2期的HDR与S期的DNA复制和M期的染色体分离是分开的。
