gp41-1C::creB::NrdJ-1N consists of amino acid residues 110-250 of P1cre, fused to the gp41-1C split intein fragment at the N-terminal end and to the NrdJ-1N split intein fragment at the C-terminal end. gp41-1C::creB::NrdJ-1N can be used as part of a tripartite split-Cre recombinase system in combination with both creA::gp41-1N and NrdJ-1C::creC (FBrf0245663). NrdJ-1N plus NrdJ-1C, and gp41-1N plus gp41-1C, each form a split intein fragment pair which show efficient protein trans-splicing, but the two pairs do not show cross-reactivity with each other or with other split intein fragments (PMID:22753413). In the tripartite split system, a functional P1cre recombinase is only reconstituted at the intersection of the expression patterns of the three split components, when trans-splicing between each of the complementary split intein fragment pairs (NrdJ-1N plus NrdJ-1C and gp41-1N plus gp41-1C respectively) results in the 'creA', 'creB' and 'creC' fragments being fused into a single polypeptide (with the split intein fragments being excised during the trans-splicing reactions) (FBrf0245663). The reconstituted recombinase is expected to have the properties of the native P1cre recombinase, with compatible target sites corresponding to the wild-type loxP site and some of its derivatives. 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).