A 1 kb PvuII-BamHI genomic fragment containing Tcra enhancer Ealpha was replaced with a sequence containing a loxP site flanked neomycin resistance gene cassette and a 700 bp XbaI-EcoRI fragment containing Igh enhancer iEmu (Rr150). The neo cassette was subsequently deleted through cre-mediated recombination. (J:82395)