The 3kb KpnI-AccI restriction sequence containing DNAse1 hypersensitivity sites 9-11 upstream of Trbd1 which form or are part of its promoter/enhancer, was replaced with a loxP site flanked neomycin resistance gene cassette, sequence for prearranged segments Trbd1/Trbj2-5 and a third loxP site. The neo cassette and the inserted gene segments were removed through subsequent cre-mediated recombination. (J:54060)