Bacterial recombination was used to insert a cre/ERT2-polyA-Frt-kanamycin-Frt cassette in-frame with the start codon of Mafb in the bacterial artificial chromosome RP23-33A18. Arabinose-induced Flpe expression in bacteria excised the kanamycin marker. The properly recombined BAC was linearized and used to produce transgenic animals. (J:193244)