φC31 integrase encoded by Streptomyces phage can mediate site-specific recombination between phage and host genomes. The recombination direction is generally considered to be accurately regulated, but the regulatory mechanisms involved are still unclear. Recently, some hyperactive mutants of φC31 integrase that can bypass the regulatory steps have been isolated and extensively studied. A putative coiled-coil region is found to play a critical role in controlling recombination direction. Further

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... analysis led us to the speculation that at least two regions in the N-terminal domain of φC31 integrase are involved in the tetrameric interfaces and that the putative coiled coil interacts with one of the regions to regulate the recombination direction.