Disruption of the IκBβ gene. (A) Schematic structure of WT IκBβ locus. Ankyrin repeats of IκBβ encoded by exons 2–5 are indicated. Furthermore, the targeting vector, the targeted IκBβ locus, the floxed IκBβ locus, and the IκBβ knock-out locus, generated by Cre recombination-mediated deletion of exons 4 and 5 are shown. Solid boxes represent exons, and lines represent introns. Neo, loxP-flanked PGK-neomycin cassette; HSV-tk, HSV-thymidine kinase gene; B, BamHI site. The length of BamHI-generated restriction fragments detected by Southern blotting with a 5′ flanking probe is indicated. Location of the 5′ flanking probe in exon 2 is shown. (B) Southern blot analysis of genomic DNA from targeted ES cells (+/3loxP), WT (+/+) mice, IκBβ^+/−, and IκBβ^−/− F₂ mice. (C) Immunoblot analysis of IκBβ, IκBα, and IκBε in whole-cell extract of WT and IκBβ^−/− (ko) spleens. The membrane was stripped and probed for β-actin to ensure equal protein loading.