Nucleotide competition assays to compare the NF-κB binding affinity of different κB sites. The indicated amounts (in picomoles) of unlabeled double-stranded oligonucleotides covering the κB sites from the IL-2Rα, c-myb, and c-mycgenes were mixed with the EMSA-reaction buffer. Nuclear extracts from day 10 BFU-E–derived cells were also added to the EMSA reaction buffer followed by the addition of 0.15 pmole (1 × 10⁵ cpm) of the ³²P-labeled κB-pd probe. The NF-κB/DNA complexes are indicated.