Structure of mutant cDNA transcripts for IκB in L428 (A) cells and KM-H2 (B) cells and scheme of the predicted truncated IκB proteins. The ankyrin repeats required for the interaction with NF-κB are indicated by filled boxes. (A) A point mutation at pos 893 of the IκB cDNA sequence in L428 cells generates a preterminal stop as indicated. (B) Top panel: 2 deletions between pos 509 and 613 and pos 618 and 640 of the IκB cDNA in KM-H2 cells result in a frame shift followed by a preterminal stop codon at pos 715. Bottom panel: Alignment of the wild-type (w.t.) cDNA sequence of IκB and the mutant IκB sequence in KM-H2 cells. Deletions and the resulting frame shift are indicated.