The L1L2_Bact_P cassette was inserted at position 155841261 of Chromosome 4 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 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 exon 2 at position 155842075. Exon 2 is thus flanked by loxP sites. A "conditional ready" (floxed) allele was created by subsequent flp-mediated recombination to remove the reporter and neo cassettes. (J:263681)