Kikuchi Y, Nash H A
J Biol Chem. 1978 Oct 25;253(20):7149-57.
Bacteriophage lambda int gene is required for the integration of viral DNA into the chromosome of Escherichia coli. We have extensively purified the product of the int gene (Int) from a lysogen of E. coli that constitutively expresses this gene. Int was assayed by its ability to promote integrative recombination of supertwisted substrate DNA in vitro using a new method based on filter trapping of a recombinant product DNA. In order to catalyze integrative recombination, Int must be supplemented by other factors that can be extracted from bacterial host cells. By itself, purified Int does not demonstrate detectable endonuclease, exonuclease, or nicking-closing activities. However, Int does make stable complexes with double-stranded lambda-DNA containing an attachment site, the region at which recombination takes place. No stable complexes are observed between Int and lambda-DNA without an attachment site or between Int and DNA containing the bacterial site of integration. Int, therefore, appears to be a specificity element that relies on additional factor(s) to provide or activate the catalytic functions required for recombination.
噬菌体λ整合酶基因是病毒DNA整合到大肠杆菌染色体所必需的。我们已从组成型表达该基因的大肠杆菌溶原菌中大量纯化了整合酶基因（Int）的产物。通过一种基于重组产物DNA滤膜捕获的新方法，利用Int促进超螺旋底物DNA体外整合重组的能力来检测Int。为了催化整合重组，Int必须由可从细菌宿主细胞中提取的其他因子补充。纯化后的Int本身未表现出可检测到的内切核酸酶、外切核酸酶或切口封闭活性。然而，Int确实能与含有附着位点（重组发生区域）的双链λ-DNA形成稳定复合物。在Int与不含附着位点的λ-DNA之间或Int与含有细菌整合位点的DNA之间未观察到稳定复合物。因此，Int似乎是一种特异性元件，依赖其他因子来提供或激活重组所需的催化功能。
