分子生物学（杨君）lecture5 site-specific recombination and transposition of DNA.pptVIP

Further reading Robin Holliday（1964）提出的Holliday模型，是第一个被广泛接受的重组模型，它是通过要发生重组的2个DNA分子的2条单链在同一部位断裂，断裂的游离末端彼此交换形成异源双链，然后2条杂合单链彼此连接形成Holliday连接体。Holliday连接体一旦形成就能进行重排，从而改变链的彼此关系，形成不同的构象，构象决定了在Holliday连接体拆分时是否发生重组。Holliday连接体是所有重组模型的核心。 * * Cre is a tyrosine recombinase, which is an phage P1-encoded protein, functioning to circularize the linear phage genome during infection. The recombination sites of Cre is lox sites. Cre-lox is sufficient for recombination Biological roles of site-specific recombination Many phage insert their DNA into the host chromosome during infection using this recombination mechanism. Example: l phage Alter gene expression. Example: Salmonella Hin recombinase (沙门氏菌的Hin重组酶通过将一个细菌染色体片段倒位，控制两组基因中哪一组被表达, not discussed in the class) Maintain the structural integrity of circular DNA molecules during cycles of DNA replication. Example: resolvase(解离酶) that resolves dimer to monomer Ch11 重组与转座 转 座 位点特异性重组 重 组 小 结 The general themes of site-specific recombination All reactions depend critically on the assembly of the recombinase protein on the DNA and bring together of the two recombination sites Some recombination requires only the recombinase and its recognition sequence for such an assembly; some requires accessory proteins including Architectural Proteins that bind specific DNA sequences and bend the DNA. Ch11 重组与转座 转 座 位点特异性重组 重 组 小 结 l integrase works with IHF and Xis to integrate/excise the phage genome into/from the bacterial chromosome The outcome of l bacteriophage infection of a host bacterium Establishment of the lysogenic state (溶源): requires the integration（整合） of phage DNA into host chromosome lytic growth （裂解）is the growth stage of multiplication of the independent phage DNA that requires the excision （切除）of the integrated phage DNA from the host genome. Ch11 重组与转座 转 座 位点特异性重组 重 组 小 结 Bacterial genome Phage genome Crossover regions Int (l-encoded integrase, a tyrosine recombinase) Xis (l-encoded excisionase)