Inactivation of the mouse ATF1 gene by gene targeting. (A) Shown is part of the ATF1 locus with exons 3 to 7 (black boxes) encoding portions of the kinase-inducible domain (exon 3) and all of the leucine zipper domain (exon 7) (top). Targeting construct containing a 3.8-kb 5′ homology and a 1.6-kb 3′ homology fragment inserted into the pHM3 vector is shown (middle). The targeted ATF1 gene is shown at bottom. lacZ-neo, β-galactosidase/neomycin-resistance cassette; Bg, BglII; E, EcoRI. (B) Top, PCR genotyping of genomic DNA isolated from embryos of heterozygous intercrosses. Detection of the wild-type allele corresponds to a 260-bp fragment, and the mutant allele corresponds to a 420-bp fragment. Bottom, Western blot analysis of nucleus extracts of kidney, liver, and testis shows clear loss of ATF1 in tissues of ATF1−/− mice. (C) Whole-mount β-galactosidase stainings of ATF1+/− and CREB+/− embryos. LacZ staining confirms the expression pattern of ATF1 and CREB revealed by immunohistochemistry (Fig. 1).