Targeting vector from IKMC Project CSD30881 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 5. The critical exon 5 is thus flanked by loxP sites. The lacZ sequence and selection cassette were removed via flp-mediated recombination, leaving exon 5 floxed.