Yu X, Egelman E H
Department of Cell Biology and Neuroanatomy, University of Minnesota Medical School, Minneapolis 55455.
J Mol Biol. 1993 May 5;231(1):29-40. doi: 10.1006/jmbi.1993.1254.
The RecA protein of Escherichia coli, as a result of DNA damage, catalyzes the cleavage of its own repressor, the LexA protein, and thereby initiates the SOS response. Using a non-cleavable LexA mutant, we have obtained a co-complex of both the RecA and LexA proteins on DNA. Mass analysis using scanning transmission electron microscopy suggests that the site size of the LexA repressor on RecA is two, which would be consistent with a nearest-neighbor exclusion model for binding. Three-dimensional reconstruction of electron micrographs of these filaments shows that the LexA protein is bound in the deep groove of the RecA filament, with two strong regions of contact that span adjacent RecA protomers within the filament. One contact is consistent with a proposed LexA binding site in the RecA crystal structure. The other contact maps onto a region that has been postulated to be a second DNA-binding site within RecA, which can explain the inhibition of RecA cleavage of LexA by excess DNA.
由于DNA损伤，大肠杆菌的RecA蛋白催化其自身的阻遏物LexA蛋白的裂解，从而启动SOS反应。利用一种不可裂解的LexA突变体，我们在DNA上获得了RecA和LexA蛋白的共复合物。使用扫描透射电子显微镜进行的质量分析表明，LexA阻遏物在RecA上的位点大小为两个，这与结合的最近邻排斥模型一致。这些细丝的电子显微照片的三维重建显示，LexA蛋白结合在RecA细丝的深沟中，有两个跨越细丝内相邻RecA原聚体的强接触区域。一个接触点与RecA晶体结构中提出的LexA结合位点一致。另一个接触点映射到一个被假定为RecA内第二个DNA结合位点的区域，这可以解释过量DNA对LexA的RecA裂解的抑制作用。
