涉及DNA的很多交易都产生一个单链中间体,它受ssDNA结合蛋白(SSB蛋白)保护而不会被降解。在保护DNA的同时,这种蛋白需要允许DNA快速接触其他蛋白,如聚合酶或修复因子,以便随后进行DNA处理。允许SSB与ssDNA保持牢固结合,同时允许DNA接触其他蛋白的一个机制,该机制已在对大肠杆菌的这种蛋白所进行的一项单分子荧光共振能量转移研究中被发现。这种SSB是一个四聚物,将ssDNA包裹在其外围。令人吃惊的是,它能通过沿ssDNA进行随机行走来迁移,以便使其能够重新定位,尽管它仍保持紧紧结合的状态。(生物谷Bioon.com)
生物谷推荐原始出处:
Nature 461, 1092-1097 (22 October 2009) | doi:10.1038/nature08442
SSB protein diffusion on single-stranded DNA stimulates RecA filament formation
Rahul Roy1,2,5, Alexander G. Kozlov3, Timothy M. Lohman3 & Taekjip Ha1,2,4
1 Center for Biophysics and Computational Biology,
2 Department of Physics and Center for the Physics of Living Cells, University of Illinois, Urbana-Champaign, Illinois 61801, USA
3 Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St Louis, Missouri 63110, USA
4 Howard Hughes Medical Institute, Urbana, Illinois 61801, USA
5 Present address: Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
Correspondence to: Taekjip Ha1,2,4 Correspondence and requests for materials should be addressed to T.H.
Single-stranded DNA generated in the cell during DNA metabolism is stabilized and protected by binding of ssDNA-binding (SSB) proteins. Escherichia coli SSB, a representative homotetrameric SSB, binds to ssDNA by wrapping the DNA using its four subunits. However, such a tightly wrapped, high-affinity protein–DNA complex still needs to be removed or repositioned quickly for unhindered action of other proteins. Here we show, using single-molecule two- and three-colour fluorescence resonance energy transfer, that tetrameric SSB can spontaneously migrate along ssDNA. Diffusional migration of SSB helps in the local displacement of SSB by an elongating RecA filament. SSB diffusion also melts short DNA hairpins transiently and stimulates RecA filament elongation on DNA with secondary structure. This observation of diffusional movement of a protein on ssDNA introduces a new model for how an SSB protein can be redistributed, while remaining tightly bound to ssDNA during recombination and repair processes.