涉及DNA的很多交易都產生一個單鏈中間體,，它受ssDNA結合蛋白（SSB蛋白）保護而不會被降解,。在保護DNA的同時,，這種蛋白需要允許DNA快速接觸其他蛋白，如聚合酶或修復因子,，以便隨后進行DNA處理,。允許SSB與ssDNA保持牢固結合，同時允許DNA接觸其他蛋白的一個機制,，該機制已在對大腸桿菌的這種蛋白所進行的一項單分子熒光共振能量轉移研究中被發(fā)現,。這種SSB是一個四聚物，將ssDNA包裹在其外圍,。令人吃驚的是,，它能通過沿ssDNA進行隨機行走來遷移，以便使其能夠重新定位,，盡管它仍保持緊緊結合的狀態(tài),。（生物谷Bioon.com）
生物谷推薦原始出處：
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.
