Integrase is necessary for integration of the phage into the host genome by site-specific recombination. In conjunction with excisionase, integrase is also necessary for excision of the prophage from the host genome. Bacteriophage 434 is a lysogenic phage that shares extensive DNA homology with bacteriophage lambda. It inserts its DNA into the E.coli chromosome at or near the lambda insertion site. Complementation of integration functions between the two phages has been demonstrated. Belongs to the 'phage' integrase family.