Ralf Christine, Hickson Ian D, Wu Leonard
Cancer Research UK Laboratories, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, University of Oxford, Oxford OX3 9DS, United Kingdom.
J Biol Chem. 2006 Aug 11;281(32):22839-46. doi: 10.1074/jbc.M604268200. Epub 2006 Jun 8.
Homozygous inactivation of BLM gives rise to Bloom's syndrome, a disorder associated with genomic instability and cancer predisposition. BLM encodes a member of the RecQ DNA helicase family that is required for the maintenance of genome stability and the suppression of sister-chromatid exchanges. BLM has been proposed to function in the rescue of replication forks that have collapsed or stalled as a result of encountering lesions that block fork progression. One proposed mechanism of fork rescue involves regression in which the nascent leading and lagging strands anneal to create a so-called "chicken foot" structure. Here we have developed an in vitro system for analysis of fork regression and show that BLM, but not Escherichia coli RecQ, can promote the regression of a model replication fork. BLM-mediated fork regression is ATP-dependent and occurs processively, generating regressed arms of >250 bp in length. These data establish the existence of a eukaryotic protein that could promote replication fork regression in vivo and suggest a novel pathway through which BLM might suppress genetic exchanges.
BLM基因的纯合失活会导致布卢姆综合征，这是一种与基因组不稳定和癌症易感性相关的疾病。BLM编码RecQ DNA解旋酶家族的一员，该家族成员对于维持基因组稳定性和抑制姐妹染色单体交换是必需的。有人提出BLM在挽救因遇到阻碍叉状进展的损伤而坍塌或停滞的复制叉中发挥作用。一种提出的叉状挽救机制涉及回归，即新生的前导链和滞后链退火形成所谓的“鸡爪”结构。在这里，我们开发了一种用于分析叉状回归的体外系统，并表明BLM，而不是大肠杆菌RecQ，可以促进模型复制叉的回归。BLM介导的叉状回归是ATP依赖的，并且持续发生，产生长度大于250 bp的回归臂。这些数据证实了一种真核蛋白的存在，该蛋白可能在体内促进复制叉回归，并提示了BLM可能抑制基因交换的新途径。
