The L1L2_gt0 cassette was inserted at position 136491938 of Chromosome 1 upstream of the critical exon(s) (Build 37). The cassette is composed of an FRT flanked lacZ/neomycin sequence followed by a loxP site. An additional loxP site is inserted downstream of the targeted exon(s) at position 136492740. The critical exon(s) is/are thus flanked by loxP sites. A "conditional ready" (floxed) allele was created by flp recombinase expression in mice carrying this allele. (J:155845, J:173534)