The L1L2_Bact_P cassette was inserted upstream of the targeted exon. The cassette is composed of an FRT site followed by a splice acceptor site, IRES, a 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, an SV40 polyA, a second FRT site and a second loxP site. A third loxP site is inserted downstream of the targeted exon. The targeted exon is thus flanked by loxP sites. Cre mediated recombination removed the targeted exon creating a reporter knockout allele. 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