An attempt to insert a 5 loxP site between exons 1 and 2 and a 3 loxP site between exons 3 and 4 of the gene was made but an unexpected recombination event resulted in insertion of a single loxP site and the neomycin selection cassette upstream of exon 4, leading to disruption of the endogenous Ybx3 locus. (J:269044)