loxP-S 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 identical to loxP except that the first two nucleotides in the 5' inverted repeat are missing (FBrf0211848). It thus consists of an 8bp asymmetric spacer sequence flanked by a pair of inverted repeats of 11bp and 13bp respectively. Recombination occurs between a pair of target sites oriented in the same direction; the inverted repeats 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). loxP-S is compatible as a target site for the native P1cre recombinase (FBrf0211848).