Shi Q, Thresher R, Sancar A, Griffith J
Department of Biochemistry and Biophysics, University of North Carolina School of Medicine, Chapel Hill 27599.
J Mol Biol. 1992 Jul 20;226(2):425-32. doi: 10.1016/0022-2836(92)90957-l.
Nucleotide excision repair in Escherichia coli is initiated by the UvrA, UvrB and UvrC proteins. UvrA is the damage recognition subunit, makes an A2B1 complex with the targeting subunit UvrB, and the complex binds to the lesion site; UvrA dissociates leaving behind a very stable UvrB-DNA complex that is recognized by the trigger subunit, UvrC, and the ensuing UvrB-UvrC heterodimer makes two incisions, one on either side of the lesion. Using electron microscopy, we investigated the structures of these early A, A-B intermediates on DNA containing ultraviolet light photoproducts. UvrA, which is known to bind to DNA as a dimer and produce a DNase I footprint of 33 base-pairs does not change the trajectory of DNA appreciably. The A2B1 complex clearly shows a bipartite structure and its effect on the trajectory of the DNA was not consistently straight or kinked. In contrast, the DNA in the preincision UvrB-DNA complex appears to be severely kinked; 43% of the molecules are bent by 80 degrees or more, with an average bending angle of 127 degrees. It appears that protein-induced bending is an important step on the pathway leading to excision of the damaged nucleotide by (A)BC excinuclease.
大肠杆菌中的核苷酸切除修复由UvrA、UvrB和UvrC蛋白启动。UvrA是损伤识别亚基，与靶向亚基UvrB形成A2B1复合物，该复合物结合到损伤位点；UvrA解离，留下非常稳定的UvrB-DNA复合物，该复合物被触发亚基UvrC识别，随后形成的UvrB-UvrC异二聚体在损伤两侧各进行一次切割。我们使用电子显微镜研究了这些早期A、A-B中间体在含有紫外线光产物的DNA上的结构。已知以二聚体形式结合到DNA上并产生33个碱基对的DNase I足迹的UvrA，不会明显改变DNA的轨迹。A2B1复合物清楚地显示出二分结构，其对DNA轨迹的影响并不总是呈直线或弯曲状。相比之下，切割前的UvrB-DNA复合物中的DNA似乎严重弯曲；43%的分子弯曲80度或更大，平均弯曲角度为127度。看来蛋白质诱导的弯曲是由（A）BC核酸外切酶切除受损核苷酸的途径中的一个重要步骤。
