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. Homotetramer. Interacts (via N-terminus) with the excisionase (via C-terminus) (PubMed:12832614). Part of the excision complex made of the integrase tetramer, IHF, Fis and Xis. Belongs to the 'phage' integrase family.