The L1L2_Bact_P cassette was inserted at position 133260405 of Chromosome 4 upstream of the critical exons 3 to 7 (Build GRCm39). The cassette is composed of an FRT site followed by lacZ sequence and a loxP site. This first loxP site is followed by a neomycin resistance gene under the control of the human beta-actin promoter, SV40 polyA, a second FRT site and a second loxP site. A third loxP site is inserted downstream of the targeted exons 3-7 at position 133263632. The critical exons 3 to 7 are thus flanked by loxP sites. Flp-mediated recombination removed the lacZ and neomycin resistance gene creating a âconditional readyâ exon 3-7 floxed allele. Information on targeting strategies used for this and other IKMC alleles can be found at http://www.informatics.jax.org/mgihome/nomen/IKMC_schematics.shtml.