The C terminus of the NF-χB p50 precursor and an IχB isoform contain transcription activation domains

The p50 subunit of the NF-kappa B transcription complex is derived from the N-terminal half of a larger precursor protein, p105. Although a fair amount is known about functions located within the p50 sequences, less is known about the C-terminal half of p105. In this report, we have identified a potent transcription activation domain located in the C terminus of mouse p105. In addition, the I kappa B beta proteins chicken p40 and human MAD-3, proteins that are related to the p105 C terminus, strongly activated transcription in chicken cells and yeast when fused to GAL4 DNA-binding sequences. Furthermore, chicken p40 is primarily located in the nucleus of chicken cells when overexpressed from a retroviral vector. Our results suggest novel models for the function and regulation of NF-kappa B transcription complexes.