中文摘要：

E.coli解旋酶Ⅱ（UvrD）是一种在甲基定向错配修复（methyl-directed mismatchrepair,MMR）和核苷酸切除修复（nucleotide excisionrepair,NER）中起重要作用的3′→5′解旋酶.本研究对大肠杆菌的UvrD进行了重组表达和纯化,并检测其ATP酶比活性（87U/mg）.利用表面等离子共振（surface plasmon resonance,SPR）方法实时检测了UvrD与同源双链DNA分子（homoduplex DNA）和异源双链DNA分子（heteroduplex DNA）结合的动态过程以及镁离子对此过程的影响.结果显示,UvrD与DNA的平衡解离常数在10^-7mol/L水平.DNA分子中错配碱基的存在,在一定程度上影响了二者的结合,而镁离子不是两者结合的必要因素.本研究还利用原子力显微镜（atomic force microscopy,AFM）方法在单分子水平上观察到UvrD将双链DNA解链形成单链DNA的中间体.此研究得到的UvrD与DNA结合的动力学信息数据以及解螺旋中间体的单分子可视化,为进一步深入研究UvrD在修复过程中的作用机制奠定了基础.

英文摘要：

E. coli helicase Ⅱ（UvrD）, which is classified as a 3′ to 5′ helicase, plays essential roles in methyl-directed mismatch repair （MMR） and nucleotide excision repair （NER）. In this report, recombinant UvrD was expressed and purified, and its ATPase specific catalytic activity was determined to be 87 U/mg, The kinetics and affinity of UvrD interactions with homo-duplex DNA and hetero-duplex DNA were also investigated using surface plasmon resonance （SPR） technology. The equilibrium dissociation constants of UvrD and DNA were evaluated to be in the 10^-7 mol/L range. Unwound DNA intermediate following UvrD treatments were observed by atomic force microscopy （AFM） at the level of single-molecule resolution. The results have shown that mismatched base pairs could affect the binding of UvrD to DNA, and Mg^2＋ was not necessary for this process. Our results have provided valuable information that will help further investigations of the molecular mechanism（s） in UvrD-mediated mismatch repair process.