Mu D, Sancar A
Department of Biochemistry and Biophysics, School of Medicine, CB 7260, University of North Carolina, Chapel Hill, North Carolina 27599-7260, USA.
J Biol Chem. 1997 Mar 21;272(12):7570-3. doi: 10.1074/jbc.272.12.7570.
In humans, DNA lesions such as pyrimidine dimers in the template strand of genes transcribed by RNA polymerase II are repaired faster than those in the coding strand and nontranscribed regions of the genome. This phenomenon, referred to as transcription-coupled repair (i) requires active transcription, (ii) does not require the XPC gene product which is essential for general/basal repair reactions, and (iii) requires the CSA and CSB proteins. We have developed an in vitro model system that consists of purified human excision repair factors and a DNA substrate analogous to a transcription bubble terminating at a cyclobutane thymine dimer. In this system the thymine dimer was excised independent of XPC. Furthermore, the thymine dimer in the bubble-containing substrate was removed approximately 3-fold faster by the excision repair nuclease reconstituted with or without XPC, compared with the removal of thymine dimer from a base paired duplex by the entire set of excision nuclease factors. These results provide important insight into the mechanism of transcription-coupled repair in humans.
在人类中，RNA聚合酶II转录的基因模板链中的DNA损伤，如嘧啶二聚体，比基因组编码链和非转录区域中的损伤修复得更快。这种现象被称为转录偶联修复，（i）需要活跃转录，（ii）不需要对一般/基础修复反应至关重要的XPC基因产物，以及（iii）需要CSA和CSB蛋白。我们开发了一种体外模型系统，该系统由纯化的人类切除修复因子和类似于终止于环丁烷胸腺嘧啶二聚体的转录泡的DNA底物组成。在这个系统中，胸腺嘧啶二聚体的切除不依赖于XPC。此外，与通过整套切除核酸酶因子从碱基配对双链体中去除胸腺嘧啶二聚体相比，用或不用XPC重组的切除修复核酸酶从含泡底物中去除胸腺嘧啶二聚体的速度快约3倍。这些结果为人类转录偶联修复机制提供了重要见解。
