The L1L2_Bact_P cassette was inserted at position 34845737 of Chromosome 16 upstream of the critical exon 2 (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 exon 2 at position 34846568. Exon 2 is thus flanked by loxP sites. A null/knockout allele was created by cre recombinase expression in mice carrying the tm1a allele to remove the neo selection cassette and loxP-flanked exon 2. Western blot analysis confirmed the absence of encoded protein in E9.5 homozygous mutant embryos. 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