The candidate proto-oncogene bcl-3 encodes a transcriptional coactivator that activates through NF-kappa B p50 homodimers.

The candidate proto-oncogene bcl-3 encodes a protein that shares structural features with I kappa B-alpha and other proteins that bind to members of the Rel protein family. Here, we show that in contrast to the inhibitory activity of I kappa B-alpha, the bcl-3 gene product superactivates NF-kappa B p50 homodimer-mediated gene expression both in vivo and in vitro. BCL-3 protein can, as well, selectively associate with p50 homodimers in the presence of DNA containing a kappa B motif. These results strongly suggest that BCL-3 can act as a transcriptional coactivator, acting through DNA-bound p50 homodimers.