The L1L2_Bact_P cassette was inserted at position 29904379 of Chromosome 17 upstream of the critical exon(s) (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(s) at position 29905269. Exon 9 is thus flanked by loxP sites. The"conditional ready" (floxed) allele was created by flp recombinase expression in mice carrying the knockout-first allele.