The L1L2_Bact_P cassette is composed of an FRT site followed by lacZ sequence and a loxP site. This first loxP site is followed by neomycin resistance gene under the control of the human beta-actin promoter, SV40 polyA, a second FRT site and a second loxP site. The FRT-lacZ-loxP-neo-FRT-loxP cassette is introduced into intron 19 followed by a loxP site placed in intron 23. Flp-mediated recombination excised the lacZ and neomycin features, leaving exons 20-23 flanked by loxP sites. (J:229436)