The L1L2_Bact_P cassette was inserted at position 53521813 of Chromosome 19 upstream of 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 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 53522677. The critical exon 2 is thus flanked by loxP sites. A null/knockout allele was created by flp and cre recombinase expression in mice carrying this allele to remove the lacZ sequence, neo selection cassette and the loxP-flanked exon 2.