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 that includes residues 1-64 and is responsible for binding the arm-type sites of attP, and a C-terminal domain (CTD) that binds the lower affinity core-type sites and contains the catalytic site. The CTD can be further divided into the core-type binding domain (residues 65-169) and the catalytic core domain (170-356), the later representing this entry. The catalytic core adopts an alpha3-beta3-alpha4 fold, where one side of the beta sheet is exposed.
The recombinases Cre from phage P1, 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 . The structural fold of their catalytic core domains resemble that of Lambda integrase
The catalytic core of the eukaryotic DNA topoisomerase I shares significant structural similarity with the bacteriophage family of DNA integrases . Topoisomerases I promote the relaxation of DNA superhelical tension by introducing a transient single-stranded break in duplex DNA and are vital for the processes of replication, transcription, and recombination.