Phage integrases are enzymes that mediate unidirectional site-specific recombination between two DNA recognition sequences, the phage attachment site, attP, and the bacterial attachment site, attB . Integrases may be grouped into two major families, the tyrosine recombinases and the serine recombinases, based on their mode of catalysis. Tyrosine family integrases, such as lambda integrase, utilise a catalytic tyrosine to mediate strand cleavage, tend to recognize longer attP sequences, and require other proteins encoded by the phage or the host bacteria.
The 356 amino acid lambda integrase consists of two domains: an N-terminal domain (NTD) that includes residues 1 - 64 and is responsible for binding the arm-type sites of attP, and a C-terminal domain that binds the lower affinity core-type sites and contains the catalytic site. The NTD adopts a 4-5 helical bundle fold with two orthogonally packed alpha-hairpins.
The recombinases Cre from P1 phage, XerD from Escherichia coli, and Flp from yeast are members of the tyrosine recombinase family, and have a two-domain motif resembling that of lambda integrase, as well as sharing a conserved binding mechanism [12560475, 16139195].
The phage integrase NTD is almost always found with the signature that defines the phage integrase family (see )