Ristic D, Wyman C, Paulusma C, Kanaar R
Department of Cell Biology and Genetics, Center for Biomedical Genetics, Erasmus University Rotterdam, PO Box 1738, 3000 DR Rotterdam, The Netherlands.
Proc Natl Acad Sci U S A. 2001 Jul 17;98(15):8454-60. doi: 10.1073/pnas.151056798.
Proper maintenance and duplication of the genome require accurate recombination between homologous DNA molecules. In eukaryotic cells, the Rad51 protein mediates pairing between homologous DNA molecules. This reaction is assisted by the Rad54 protein. To gain insight into how Rad54 functions, we studied the interaction of the human Rad54 (hRad54) protein with double-stranded DNA. We have recently shown that binding of hRad54 to DNA induces a change in DNA topology. To determine whether this change was caused by a protein-constrained change in twist, a protein-constrained change in writhe, or the introduction of unconstrained plectonemic supercoils, we investigated the hRad54--DNA complex by scanning force microscopy. The architecture of the observed complexes suggests that movement of the hRad54 protein complex along the DNA helix generates unconstrained plectonemic supercoils. We discuss how hRad54-induced superhelical stress in the target DNA may function to facilitate homologous DNA pairing by the hRad51 protein directly. In addition, the induction of supercoiling by hRad54 could stimulate recombination indirectly by displacing histones and/or other proteins packaging the DNA into chromatin. This function of DNA translocating motors might be of general importance in chromatin metabolism.
基因组的正确维护和复制需要同源DNA分子之间进行精确的重组。在真核细胞中，Rad51蛋白介导同源DNA分子之间的配对。该反应由Rad54蛋白协助。为深入了解Rad54的功能，我们研究了人类Rad54（hRad54）蛋白与双链DNA的相互作用。我们最近发现，hRad54与DNA的结合会引起DNA拓扑结构的变化。为确定这种变化是由蛋白质限制的扭曲变化、蛋白质限制的缠绕变化还是引入无限制的螺旋超螺旋引起的，我们通过扫描力显微镜研究了hRad54-DNA复合物。观察到的复合物结构表明，hRad54蛋白复合物沿DNA螺旋的移动会产生无限制的螺旋超螺旋。我们讨论了hRad54在目标DNA中诱导的超螺旋应力如何可能直接通过hRad51蛋白促进同源DNA配对。此外，hRad54诱导的超螺旋化可能通过取代组蛋白和/或将DNA包装成染色质的其他蛋白质来间接刺激重组。DNA转运马达的这种功能在染色质代谢中可能具有普遍重要性。
