Cre-recombinase is a 38 kDa DNA recombinase derived from the P1 bacteriophage. It is highly specific for a 34 bp DNA sequence (loxP) found in P1 DNA. It catalyzes site-specific recombination between two 34-base-pair LOXP sites. Its role is to maintain the phage genome as a monomeric unit-copy plasmid in the lysogenic state. It is homotetramer when bound to DNA and belongs to the "phage" integrase family.