Igha promoter Rr361 (~840 bp), (part of) the last intron and exon of human hemoglobin subunit beta (~1100 bp) and a loxP site flanked neomycin resistance gene cassette were inserted downstream of super-enhancer 3'RR (Rr152), between it and Igh super-insulator Rr363. The neo cassette was removed through subsequent cre-mediated recombination. (J:242276)