Preincubation without attB DNA inhibits In Vitro Integrative Recombination of P 1 Mutant attP DNA of Bacteriophage Lambda

The lambda integrase (lnt) is believed to bind to several arm and core sites of attP DNA in order to facilitate intasome formation. We have done systematic mutagenic analysis on all 5 arm sites and found that P1 is absolutely required for integration while P2 is not. We also found that all 3 P' arm sites(P'1, P'2, and P'3) are required for efficient integrative recombination. P'1, which is an important binding site for excision, also seems to be crucial for integration when preincubation of attP DNA with Int and IHF is performed before recombination. Preincubation assay revealed that preincubation with Int and IHF improved the efficiency of recombination of wild type attP DNA and demolished recombinations of P'1 mutant attP DNAs.