FIG. 1.

PAC1-dependent proteasome biogenesis is essential for mammalian development. (A) Strategy for the mutation of Psmg1 gene. The genomic region of the wild-type Psmg1 locus (+), the Psmg1 targeting vector, the structures of the mutated Psmg1 gene (M), the floxed gene in which the neomycin cassette (Neo) removed by flippase-mediated recombination (F), and the knockout allele in which exon 2 was deleted by Cre-mediated recombination [Δexon2 (−)] are depicted. The numbered black boxes are Psmg1 exons. The open arrowheads and circles indicate loxP and FRT sites. The probe for Southern blot analysis is shown as a gray box. DNA fragments detected by Southern blot analysis after BamHI digestion are shown. DTA, diphtheria toxin fragment A. (B) Southern blot analysis of genomic DNAs extracted from ES cells of the indicated genotypes. (C) Psmg1^+/+ or Psmg1^+/− (left) and Psmg1^−/− (right) embryos in the uterus at E6.0 (top) and E6.5 (bottom) were morphologically identified by hematoxylin-eosin (HE) staining followed by immunofluorescent staining with anti-PAC1 antibody (middle). The signal shown with an asterisk in the immunostaining of Psmg1^−/− embryo corresponds to eosinophilic structures seen outside the embryo in HE staining and probably is due to nonspecific staining.