Position and direction of strand exchange in bacteriophage HK022 integration.

The positions of the endonucleolytic cleavages promoted by the integrase protein (Int) of coliphage HK022 within its attB site were determined. The protein catalyses a staggered cut, which defines an overlap sequence of 7 bp within the core site. The overlap region is at the center of symmetry of a palindromic sequence which appears in all four putative att core binding sites for Int. We confirm that the order of strand exchange is similar to that in phage lambda.