Department of Physics and Center for the Physics of Living Cells, University of Illinois, Urbana-Champaign, IL 61801, USA.
Cell. 2011 Jul 22;146(2):222-32. doi: 10.1016/j.cell.2011.06.036.
SSB proteins bind to and control the accessibility of single-stranded DNA (ssDNA), likely facilitated by their ability to diffuse on ssDNA. Using a hybrid single-molecule method combining fluorescence and force, we probed how proteins with large binding site sizes can migrate rapidly on DNA and how protein-protein interactions and tension may modulate the motion. We observed force-induced progressive unraveling of ssDNA from the SSB surface between 1 and 6 pN, followed by SSB dissociation at ∼10 pN, and obtained experimental evidence of a reptation mechanism for protein movement along DNA wherein a protein slides via DNA bulge formation and propagation. SSB diffusion persists even when bound with RecO and at forces under which the fully wrapped state is perturbed, suggesting that even in crowded cellular conditions SSB can act as a sliding platform to recruit and carry its interacting proteins for use in DNA replication, recombination and repair.
SSB 蛋白结合并控制单链 DNA（ssDNA）的可及性，这可能是由于它们能够在 ssDNA 上扩散。我们使用荧光和力相结合的混合单分子方法，研究了具有较大结合位点大小的蛋白质如何在 DNA 上快速迁移，以及蛋白质-蛋白质相互作用和张力如何调节运动。我们观察到在 1 到 6 pN 之间，ssDNA 从 SSB 表面逐渐解开，随后在约 10 pN 时 SSB 解离，并获得了蛋白质沿 DNA 运动的蠕动机制的实验证据，其中蛋白质通过 DNA 凸起的形成和传播进行滑动。即使在与 RecO 结合以及在完全包裹状态受到干扰的力下，SSB 扩散仍然存在，这表明即使在拥挤的细胞条件下，SSB 也可以作为滑动平台，招募并携带与其相互作用的蛋白质，用于 DNA 复制、重组和修复。
