The cathepsin G (CG) locus and targeting strategy. (A) The structures of the murine cathepsin G gene and the targeting vector used to create homologous recombinants are shown. The PGK-neo cassette was inserted in the antisense orientation with respect to the cathepsin G gene. The structure of the targeted locus and the sizes of fragments detected by probe A (which is completely external to the targeting construct) and probe B (the PGK-neo cassette) are shown. (B) Southern blot analysis of tail DNA from the progeny of a cross between cathepsin G+/− animals. Genomic DNA was cleaved with Xba I and the blot was hybridized with probe A. The positions of the wild-type (7.6 kb) allele and the targeted (2.2 kb) allele are shown.