GP Ibβ gene structure and targeted disruption. (A) The mouse GP Ibβ gene is schematically presented as it spans a portion of GenBank accession no. AC008019. The GP Ibβ gene is adjacent to a second gene, SEPT5, whose exon arrangement is shown as open boxes. The GP Ibβ gene is composed of 2 exons (boxes I and II), with most of the coding sequence present in exon 2 (black box). E indicates EcoRI; H, HindIII; X, XhoI; and B, BamHI. (B) The structure of a targeting vector to disrupt the GP Ibβ gene is shown directly under the corresponding genomic region depicted in panel A. The pBS/KS-vector is shown as a dashed line. N indicates NotI. (C) Successful homologous recombination in mouse embryonic stem (ES) cells results in the replacement of an 18-kb EcoRI restriction fragment with a 12-kb EcoRI fragment and the structure of a targeted allele is shown. The position of a radiolabeled probe used to identify clones with homologous recombination is shown. (D) Southern blot analysis of 2 clones (166^ES and 182^ES) with the altered EcoRI restriction fragment pattern and 2 clones (32^ES and 2^ES) with the 2 copies of a wild-type allele. (E) Germ line transmission of 166^ES cells was obtained producing GP Ibβ^Het mice. The breeding of GP Ibβ^Het mice produced the expected 3 genotypes and shown is a representative Southern blot of HindIII-restricted DNA revealing the wild-type GP Ibβ gene (5.6 kb) and the targeted allele (6.6 kb) present in each respective genotype.