The L1L2_Bact_P cassette was inserted at position 73753908 of Chromosome 13 upstream of the critical exon 3 (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 3 at position 73754758. Exon 3 is thus flanked by loxP sites. Flp-mediated recombination removed the reporter and selection cassettes and left exon 3 floxed. (J:265892)