Wu Leonard, Bachrati Csanad Z, Ou Jiongwen, Xu Chang, Yin Jinhu, Chang Michael, Wang Weidong, Li Lei, Brown Grant W, Hickson Ian D
Cancer Research UK, Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DS, United Kingdom.
Proc Natl Acad Sci U S A. 2006 Mar 14;103(11):4068-73. doi: 10.1073/pnas.0508295103. Epub 2006 Mar 6.
BLM encodes a member of the highly conserved RecQ DNA helicase family, which is essential for the maintenance of genome stability. Homozygous inactivation of BLM gives rise to the cancer predisposition disorder Bloom's syndrome. A common feature of many RecQ helicase mutants is a hyperrecombination phenotype. In Bloom's syndrome, this phenotype manifests as an elevated frequency of sister chromatid exchanges and interhomologue recombination. We have shown previously that BLM, together with its evolutionarily conserved binding partner topoisomerase IIIalpha (hTOPO IIIalpha), can process recombination intermediates that contain double Holliday junctions into noncrossover products by a mechanism termed dissolution. Here we show that a recently identified third component of the human BLM/hTOPO IIIalpha complex, BLAP75/RMI1, promotes dissolution catalyzed by hTOPO IIIalpha. This activity of BLAP75/RMI1 is specific for dissolution catalyzed by hTOPO IIIalpha because it has no effect in reactions containing either Escherichia coli Top1 or Top3, both of which can also catalyze dissolution in a BLM-dependent manner. We present evidence that BLAP75/RMI1 acts by recruiting hTOPO IIIalpha to double Holliday junctions. Implications of the conserved ability of type IA topoisomerases to catalyze dissolution and how the evolution of factors such as BLAP75/RMI1 might confer specificity on the execution of this process are discussed.
BLM编码高度保守的RecQ DNA解旋酶家族的一个成员，该家族对于维持基因组稳定性至关重要。BLM的纯合失活会导致癌症易感性疾病布卢姆综合征。许多RecQ解旋酶突变体的一个共同特征是高重组表型。在布卢姆综合征中，这种表型表现为姐妹染色单体交换和同源重组频率升高。我们之前已经表明，BLM与其进化上保守的结合伴侣拓扑异构酶IIIα（hTOPO IIIα）一起，可以通过一种称为解离的机制将含有双Holliday连接的重组中间体加工成非交叉产物。在这里，我们表明人类BLM/hTOPO IIIα复合物最近鉴定出的第三个组分BLAP75/RMI1促进hTOPO IIIα催化的解离。BLAP75/RMI1的这种活性对hTOPO IIIα催化的解离具有特异性，因为它在含有大肠杆菌Top1或Top3的反应中没有作用，这两种酶也都可以以BLM依赖的方式催化解离。我们提供证据表明BLAP75/RMI1通过将hTOPO IIIα募集到双Holliday连接来发挥作用。讨论了IA型拓扑异构酶催化解离的保守能力的意义以及诸如BLAP75/RMI1等因子的进化如何可能赋予该过程执行的特异性。
