Department of Biochemistry and Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Toronto, Ontario, Canada.
Mol Cell Biol. 2012 Aug;32(15):3054-64. doi: 10.1128/MCB.00255-12. Epub 2012 May 29.
RMI1 is a member of an evolutionarily conserved complex composed of BLM and topoisomerase IIIα (TopoIIIα). This complex exhibits strand passage activity in vitro, which is likely important for DNA repair and DNA replication in vivo. The inactivation of RMI1 causes genome instability, including elevated levels of sister chromatid exchange and accelerated tumorigenesis. Using molecular combing to analyze DNA replication at the single-molecule level, we show that RMI1 is required to promote normal replication fork progression. The fork progression defect in RMI1-depleted cells is alleviated in cells lacking BLM, indicating that RMI1 functions downstream of BLM in promoting replication elongation. RMI1 localizes to subnuclear foci with BLM and TopoIIIα in response to replication stress. The proper localization of the complex requires a BLM-TopoIIIα-RMI1 interaction and is essential for RMI1 to promote recovery from replication stress. These findings reveal direct roles of RMI1 in DNA replication and the replication stress response, which could explain the molecular basis for its involvement in suppressing sister chromatid exchange and tumorigenesis.
RMI1 是一个进化上保守的复合物的成员，该复合物由 BLM 和拓扑异构酶 IIIα（TopoIIIα）组成。该复合物在体外具有链转移活性，这对于体内的 DNA 修复和 DNA 复制可能很重要。RMI1 的失活导致基因组不稳定，包括姐妹染色单体交换水平升高和肿瘤加速形成。我们使用分子梳理技术在单分子水平上分析 DNA 复制，结果表明 RMI1 促进正常复制叉的推进。在缺乏 BLM 的细胞中，耗尽 RMI1 的细胞中的叉推进缺陷得到缓解，表明 RMI1 在促进复制延伸方面是 BLM 的下游。RMI1 与 BLM 和 TopoIIIα 一起定位于亚核焦点，以响应复制应激。该复合物的正确定位需要 BLM-TopoIIIα-RMI1 相互作用，对于 RMI1 促进从复制应激中恢复至关重要。这些发现揭示了 RMI1 在 DNA 复制和复制应激反应中的直接作用，这可以解释其参与抑制姐妹染色单体交换和肿瘤形成的分子基础。
