The knock-in contruct inserted downstream of the Emu enhancer contains a VH promoter driving B cell expression of the cDNA fusion of the 5' end of human PAX5 (exons 1 through 7) with the coding sequence of human ENL (exons 2 through 33). This fusion is present in B cell acute lymphoblastic leukemia with the translocation t(7;9)(q11;p13). Cre-mediated recombination removed the floxed neomycin resistance cassette. (J:266607)