Nucleotide Excision Repair in Escherichia Coli

许多外来试剂与DNA形成共价加合物。这些损伤可通过核苷酸切除修复系统去除，如大肠杆菌的UvrABC内切酶系统。修复的机制和效率可能取决于病变部位的DNA结构。使用补骨脂素单加合物或交联剂修饰的均质底物，DNA序列和螺旋构象将与DNA修复的体外效率有关。将对蛋白质DNA复合体和中间产物进行分析，以阐明修复的生化机制。有人建议测试交联链的修复速度是否取决于DNA构象；快速修复是否是由于UvrABC内切酶的快速切割，以及缓慢修复是否可能形成高亲和力的UvrAB-损伤核蛋白复合体，从而促进随后的较慢步骤，如重组修复。核苷酸切除DNA修复是一种自然的细胞防御机制，细胞通过这种机制使用多酶复合体来消除DNA中的各种损伤。这些DNA损伤的一个共同特征可能是局部DNA构象的扭曲，这对核苷酸切除修复酶很有吸引力，使这个酶系统表现出广泛的底物特异性。在更复杂的DNA损伤中，修复也可能需要DNA重组酶的参与。杨博士将使用多种修复酶和确定的DNA底物研究补骨脂素-DNA单加合物和交联物在纯化系统中的修复，以更好地了解这一重要细胞过程的机制。

Many foreign agents form covalent adducts with DNA. These lesions are removed by nucleotide excision repair systems such as the UvrABC endonuclease system of E. coli. The mechanism and efficiency of repair may depend on the DNA structure at the site of the lesion. Using homogeneous substrates specifically modified with a psoralen monoadduct or crosslink, DNA sequences and helix conformation will be related to the in vitro efficiency of DNA repair. Protein DNA complexes and intermediate products will be analyzed in order to formulate biochemical mechanisms of repair. It is proposed to test whether the rate of repair of a crosslink depends on the DNA conformation; whether fast repair is due to rapid incision by UvrABC endonuclease and whether slow repair may form a high affinity UvrAB-lesion nucleoprotein complex which promotes subsequent slower steps such as recombinational repair. Nucleotide Excision DNA repair is a natural cellular defense mechanism by which a cell, using multienzyme complexes rids itself of a variety of lesions in its DNA. A feature in common among these DNA lesions may be a distortion of the local DNA conformation which becomes attractive to the nucleotide excision repair enzymes, allowing this enzyme system to exhibit a broad range of substrate specificity. In more complex DNA lesions repair may also require the participation of DNA recombinant enzymes. Dr. Yeung will study the repair of psoralen-DNA monoadducts and crosslinks in purified system using a number of repair enzymes and defined DNA substrates in order to better understand the mechanism of this important cellular process.