lox2272 is an engineered recombination target site derived from the wild-type loxP site (the target site for the recombinase encoded by the cre locus of the bacteriophage P1 genome). It is composed of two 13bp inverted repeats flanking an 8bp asymmetric spacer sequence (5'-ATAACTTCGTATAaagtatccTATACGAAGTTAT-3') and contains mutations in the spacer sequence compared to loxP (PMID:9714735). 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). Since the recombinase binding sites are not altered compared to loxP, lox2272 is a target site for the native P1cre recombinase (and any engineered cre derivative which retains the native target-site specificity). Sequence homology between the spacer sequence of the two target sites is required for efficient cre-mediated recombination to occur (PMID:3457367, PMID:9714735). Thus, a lox2272 'spacer variant' site will recombine with an identical lox2272 site, but is not expected to recombine with the native loxP site or other engineered derivatives (PMID:9714735).