Department of Biochemistry & Molecular Biophysics, Columbia University, New York, NY 10032, USA.
Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, New Haven, CT 06520, USA.
Nucleic Acids Res. 2019 May 21;47(9):4694-4706. doi: 10.1093/nar/gkz186.
DNA helicases of the RecQ family are conserved among the three domains of life and play essential roles in genome maintenance. Mutations in several human RecQ helicases lead to diseases that are marked by cancer predisposition. The Saccharomyces cerevisiae RecQ helicase Sgs1 is orthologous to human BLM, defects in which cause the cancer-prone Bloom's Syndrome. Here, we use single-molecule imaging to provide a quantitative mechanistic understanding of Sgs1 activities on single stranded DNA (ssDNA), which is a central intermediate in all aspects of DNA metabolism. We show that Sgs1 acts upon ssDNA bound by either replication protein A (RPA) or the recombinase Rad51. Surprisingly, we find that Sgs1 utilizes a novel motor mechanism for disrupting ssDNA intermediates bound by the recombinase protein Rad51. The ability of Sgs1 to disrupt Rad51-ssDNA filaments may explain some of the defects engendered by RECQ helicase deficiencies in human cells.
RecQ 家族的 DNA 解旋酶在生命的三个领域中都得到了保守，并且在基因组维护中发挥着重要作用。几种人类 RecQ 解旋酶的突变导致了以癌症易感性为特征的疾病。酿酒酵母 RecQ 解旋酶 Sgs1 与人类 BLM 同源，其缺陷会导致易患癌症的布卢姆综合征。在这里，我们使用单分子成像技术，对 Sgs1 在单链 DNA（ssDNA）上的活性进行定量的机制理解，ssDNA 是 DNA 代谢各个方面的中心中间产物。我们表明，Sgs1 作用于由复制蛋白 A（RPA）或重组酶 Rad51 结合的 ssDNA。令人惊讶的是，我们发现 Sgs1 利用一种新的马达机制来破坏由重组酶蛋白 Rad51 结合的 ssDNA 中间体。Sgs1 破坏 Rad51-ssDNA 丝的能力可以解释人类细胞中 RECQ 解旋酶缺陷引起的一些缺陷。
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