Yu X, Jacobs S A, West S C, Ogawa T, Egelman E H
Department of Biochemistry and Molecular Genetics, University of Virginia Health Sciences Center, Box 800733, Charlottesville, VA 22908, USA.
Proc Natl Acad Sci U S A. 2001 Jul 17;98(15):8419-24. doi: 10.1073/pnas.111005398.
Both the bacterial RecA protein and the eukaryotic Rad51 protein form helical nucleoprotein filaments on DNA that catalyze strand transfer between two homologous DNA molecules. However, only the ATP-binding cores of these proteins have been conserved, and this same core is also found within helicases and the F1-ATPase. The C-terminal domain of the RecA protein forms lobes within the helical RecA filament. However, the Rad51 proteins do not have the C-terminal domain found in RecA, but have an N-terminal extension that is absent in the RecA protein. Both the RecA C-terminal domain and the Rad51 N-terminal domain bind DNA. We have used electron microscopy to show that the lobes of the yeast and human Rad51 filaments appear to be formed by N-terminal domains. These lobes are conformationally flexible in both RecA and Rad51. Within RecA filaments, the change between the "active" and "inactive" states appears to mainly involve a large movement of the C-terminal lobe. The N-terminal domain of Rad51 and the C-terminal domain of RecA may have arisen from convergent evolution to play similar roles in the filaments.
细菌的RecA蛋白和真核生物的Rad51蛋白都能在DNA上形成螺旋状核蛋白丝，催化两个同源DNA分子之间的链转移。然而，这些蛋白中只有ATP结合核心得以保留，并且在解旋酶和F1 - ATP酶中也发现了相同的核心。RecA蛋白的C末端结构域在螺旋状RecA丝内形成叶状结构。然而，Rad51蛋白没有RecA中发现的C末端结构域，而是有一个RecA蛋白中不存在的N末端延伸。RecA的C末端结构域和Rad51的N末端结构域都能结合DNA。我们利用电子显微镜显示，酵母和人类Rad51丝的叶状结构似乎是由N末端结构域形成的。这些叶状结构在RecA和Rad51中在构象上都是灵活的。在RecA丝内，“活性”和“非活性”状态之间的变化似乎主要涉及C末端叶状结构的大幅移动。Rad51的N末端结构域和RecA的C末端结构域可能是通过趋同进化产生的，以便在丝中发挥相似的作用。
