The NF-ϰB transcription factor induces DNA bending which is modulated by its 65-kD subunit

This study describes a novel functional property of the eukaryotic transcription factor NF-kappa B in altering the DNA structure. We observed that the binding of purified NF-kappa B to DNA was facilitated by spermine and cations which are known to promote DNA bending, and by a nick in one position at the 3'-end of the binding site. Furthermore, the position of the NF-kappa B binding sequence 5'-GGGACTTTCC-3' (kappa B motif) within circularly permutated DNA fragments had a profound influence on the mobility of NF-kappa B-DNA complexes in a gel retardation assay while the mobility of unbound DNA fragments did not depend on the position of the kappa B motif. The mobility effect was slightly reduced at increased temperature. These observations suggested that binding of NF-kappa B to DNA induces bending. The estimated bending angle induced by the 50-kD DNA binding subunit of NF-kappa B (p50) was smaller than that induced by p50 which was associated with the 65-kD non-DNA binding subunit (p65). Moreover, the presence of p65 appeared to result in a shift of the bending center from the middle towards the 3'-end of the kappa B motif. This shows a role for the p65 subunit of NF-kappa B in modulating the extent and altering the position of protein-induced DNA bending.