The L1L2_Bact_P cassette was inserted at position 41855482 of Chromosome 5 upstream of the critical exon 3 (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 exon 3 at position 41856303. The critical exon 3 is thus flanked by loxP sites. A null/knockout allele was created by flp and cre recombinase expression in mice carrying this allele to remove the lacZ sequence, neo selection exon, and exon 3. Further 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.