The Bxb1:int entry in FlyBase represents the integrase encoded by the Bxb1 mycobacteriophage (UniProtKB:Q9B086). Bxb1:int mediates recombination between two non-identical target sites, attP(Bxb1) and attB(Bxb1), each of which contains a short integration core flanked by imperfect inverted repeats. Exchange between the attP(Bxb1)/attB(Bxb1) pair results in the formation of hybrid sites that are no longer a substrate of the Bxb1:int integrase, and thus the exchange reaction driven by Bxb1:int is unidirectional (reviewed in PMID:21195181, FBrf0231034). The recombination event catalyzed by Bxb1:int results in genetic modification, the nature of which is influenced by the relative orientation (direct or inverted), and location of the two target sites. The types of possible modification include deletion of DNA, generation of chromosomal rearrangements, integration of DNA into the genome, and replacement of genetic material with that from a donor plasmid using recombination-mediated cassette exchange (RMCE) (reviewed in FBrf0231034).