The L1L2_Bact_P cassette was inserted at position 47050034 of Chromosome 4 upstream of the critical 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 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 2 at position 47050034. The critical exon 2 is thus flanked by loxP sites. Flp-mediated recombination removed the lacZ and neomycin resistance gene. Cre-mediated recombination deleted exon 2 and generated a knockout mouse. Western blot analysis confirmed the absence of protein in mouse embryonic fibroblasts.