N-terminal DNA-binding domains contribute to differential DNA-binding specificities of NF-kappa B p50 and p65.

We previously reported that either oxidation or alkylation of NF-kappa B in vitro abrogates DNA binding. We used this phenomenon to help elucidate structural determinants of NF-kappa B binding. We now demonstrate that Cys-62 of NF-kappa B p50 mediates the redox effect and lies within an N-terminal region required for DNA binding but not for dimerization. Several point mutations in this region confer a transdominant negative binding phenotype to p50. The region is highly conserved in all Rel family proteins, and we have determined that it is also critical for DNA binding of NF-kappa B p65. Replacement of the N-terminal region of p65 with the corresponding region from p50 changes its DNA-binding specificity towards that of p50. These data suggest that the N-terminal regions of p50 and p65 are critical for DNA binding and help determine the DNA-binding specificities of p50 and p65. We have defined within the N-terminal region a sequence motif, R(F/G)(R/K)YXCE, which is present in Rel family proteins and also in zinc finger proteins capable of binding to kappa B sites. The potential significance of this finding is discussed.     

The inhibitory ankyrin and activator Rel proteins.

The gene families encoding the proteins NF-kappa B, c-Rel and Dorsal, in conjunction with their respective inhibitors l kappa B, pp40, and Cactus, achieve specificity in gene regulation by means of common principles. The related activities of NF-kappa B and Dorsal are mediated by heterodimeric or homodimeric complexes of proteins containing the conserved dimerization and DNA-binding domain termed Rel. The l kappa Bs and Cactus, which share a core series of structural repeats termed ankyrin, inhibit cognate activators through differential interactions with the Rel-homology domain. Together, the inhibitory ankyrin proteins and their cognate Rel dimers probably define specific signalling pathways able to activate specific gene expression. Both gene families include proto-oncogenes, thus broadly implicating Rel/l kappa B in the control of both normal gene expression and the aberrant gene expression that makes cells cancerous.