Stx1-induced NF-κB complexes contain p50 and rel-A (p65). Nuclear extracts from Stx1-treated THP-1 cells were incubated with or without rabbit antihuman p50 or p65 antibodies for 10 minutes at room temperature before assessing NF-κB binding activity using radiolabeled oligonucleotides. The positions of supershifted bands are indicated by arrows. The specificity of binding was determined by cold oligonucleotide competition (lanes 4 and 8).