Site-specific integration of the Haemophilus influenzae bacteriophage HP1. Identification of the points of recombinational strand exchange and the limits of the host attachment site.

Isotopic transfer experiments and boundary replacement studies were used to define the size and cleavage points of the Haemophilus influenzae attB site for phage HP1 integration. The points of strand cleavage and transfer were separated by 5' extensions with a spacing or overlap region most probably 7 residues long. The complete HP1 attB site is included within an 18-base pair (bp) sequence surrounding the cleavage sites. The sequence of HP1 attB is remarkably symmetric. Two 8-bp inverted repeats surround the central residue of the 7-bp overlap sequence; this central residue is the second residue of the anticodon sequence of the H. influenzae tRNA(leu)(UUR) gene which contains attB, and this symmetric segment encodes the anticodon stem and loop.