The loxP entry in FlyBase represents the wild-type target site for the cre recombinase encoded by the bacteriophage P1 genome. The 34bp loxP site (5'-ATAACTTCGTATAatgtatgcTATACGAAGTTAT-3') is composed of two 13bp inverted repeats flanking an 8bp asymmetric spacer sequence (PMID:6954485). Recombination occurs between a pair of target sites oriented in the same direction; the 13bp repeats each act as binding sites for the recombinase, while the asymmetric 8bp spacer is the site of DNA strand exchange and determines the orientation of the target site (PMID:3856690). The recombination event catalyzed by the cre recombinase results in genetic modification, the nature of which is influenced by the relative orientation (direct or inverted), location and composition of the two target sites. The types of possible modification include deletion of DNA and generation of chromosomal rearrangements (reviewed in FBrf0231034).

PMID:17972876 demonstrates that loxP is incompatible with lox2272 in vivo (HEK cells).