The L1L2_Bact_P cassette was inserted at position 37433145 of Chromosome 16 upstream of the critical exon 6 (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 6 at position 37434039. The critical exon 6 is thus flanked by loxP sites. A conditional allele was created by flp recombinase expression in mice carrying this allele to remove the lacZ sequence and neo selection cassette, leaving exon 6 floxed.