Site-specific recombination by fC31 integrase and other large serine recombinases

Most temperate phages encode an integrase for integration and excision of the prophage. Integrases belong either to the lambda Int family of tyrosine recombinases or to a subgroup of the serine recombinases, the large serine recombinases. Integration by purified serine integrases occurs efficiently in vitro in the presence of their cognate (similar to 50 bp) phage and host attachment sites, attP and attB respectively. Serine integrases require an accessory protein, Xis, to promote excision, a reaction in which the products of the integration reaction, attL and attR, recombine to regenerate attP and attB. Unlike other directional recombinases, serine integrases are not controlled by proteins occupying accessory DNA-binding sites. Instead, it is thought that different integrase conformations, induced by binding to the DNA substrates, control protein-protein interactions, which in turn determine whether recombination proceeds. The present review brings together the evidence for this model derived from the studies on phi C31 integrase, Bxb1 integrase and other related proteins.