Generation of a conditional allele of the Dab1 gene. Exon III of the Dab1 locus (encoding residues 23-69) was selected for replacement by a Dab1 expression cassette flanked by loxP sites (triangles). The targeting vector includes the floxed Dab1 expression cassette comprised of the endogenous splice acceptor, Dab1 p80 cDNA sequences from residue 23-555, some 3' untranslated region, and a triple repeated poly(A) signal. A splice acceptor β-galactosidase reporter was placed downstream of the Dab1 expression cassette to indicate Cre-mediated recombination. The PGK-neo drug selectable marker was flanked by frt sites (circles). The PGK promoter driving diphteria toxin expression (PGK-DTA) was placed outside of the targeted region to provide negative selection against non-homologous recombinants. Arrowheads represent primers used to identify homologous recombinants, and arrows denote primers used for genotyping of Dab1 cKIneo mice. S- SacI, S2-SacII unique site, E- EcoRI, X-XbaI.