B2R corresponds to the recombinase encoded by the pSB2 plasmid of Zygosaccharomyces bailii. It recognizes the B2RT target site, with recombination occurring between a pair of these sites. The recombination event results in genetic modification, the nature of which is influenced by the relative orientation (direct or inverted), location and composition of the two recognition sites. The types of possible modification include deletion of DNA, generation of chromosomal rearrangements, integration of DNA into the genome and integration of DNA into the genome. B2R shows low toxicity in transgenic Drosophila (FBrf0214794).

B2R shows no recombinase activity towards the B3RT, KDRT or FRT target sites in an in vivo excision assay. It shows a very low cross-reactivity with the RSRT site: 0.9% of cells carrying a RSRT cassette show an excision event compared to 99.9% of cells carrying a B2RT cassette.