从分子层面上研究DNA复制体进行DNA复制的机理，可以理解最基本的生命现象，为很多与DNA复制有关的疾病的治疗提供参考。在哈佛大学医学院，申请人前期工作研究了T7DNA复制体的结构和功能，鉴定出解旋酶和聚合酶之间一个新的相互作用位点控制着DNA复制的起始，也发现解旋酶杂六聚体可以加速DNA复制，但在T7 DNA复制中，ssDNA结合蛋白（gp2.5）的很多功能和机制仍然是未知的，需进一步探索。根据最新研究进展，申请人希望探索gp2.5在链取代DNA合成中和在ssDNA杂化中的新功能和机制。预实验已经证明gp2.5可以和聚合酶一起进行链取代反应，完全颠覆了以前认为只有解旋酶和聚合酶才可以进行链取代的观点。本申请的研究将有助于进一步揭示T7的DNA复制中更深层次的分子机理，并开发具有新功能、新用途的蛋白酶。

Transfer of genetic information for most of lives is dependent on accurate DNA replication. Studies on the molecular mechanism of DNA replication by the DNA replisome in vitro can explain the fundamental phenomena of lives and provide instructions for therapies of many harmful diseases that are related to DNA replication. Till now, the replisomes of E. coli, bacteriophages T4 and T7 have been constructed in vitro and been studied extensively. At Harvard Medical School, the applicant has studied the structure，function, and interactions among the T7 replisome, discovered (i) a new interaction between helicase and DNA polymerase that controls the initiation of DNA replication, (ii) the new function of hetero-hexamer of gene 4 proteins for acceleration of DNA replication, and (iii) the functions of five Trp residues of primase in the synthesis of RNA primer. However, lots of functions and mechanism of T7 ssDNA binding protein (gp2.5) are still uncovered. According to the recent research, the applicant chooses two most important questions about gp2.5 and plans to (a) investigate the functions and molecular mechanism of strand-displacement DNA synthesis mediated by T7 gp2.5 and DNA polymerase,as well as the effect of DNA damage produced from environmental carcinogens on this DNA synthesis; and (b) study the mechanism of fast annealing of two complementary ssDNA by T7 gp2.5. The priliminary data has shown that gp2.5 CAN do strand-displacement DNA synthesis together with DNA polymerase, which completely innovate the previous knowledge that only helicase and DNA polymerase can do this reaction. This research will help us not only to further understand the fundamental molecular mechanism of DNA replication, but also to discover enzymes that have new functions and new applications.