The L1L2_Bact_P cassette was inserted at position 75414469 of Chromosome 1 upstream of the critical exon 5 (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 5 at position 75415288. The critical exon 5 is thus flanked by loxP sites. A "conditional ready" (floxed) allele can be created by flp recombinase expression in mice carrying this allele. Subsequent cre expression results in exon 5 removal and a knockout mouse. Immunoblot analysis confirmed absence of protein.