Transcriptional regulation of the HIV-1 promoter by NF-KB in vitro

NF-KB, purified from HeLa cell cytosol, and a recombinant p50 subunit of NF-KB alone (expressed in and purified from bacteria) both stimulated transcription from the HIV-1 promoter in vitro (at least up to 15-fold]. A deletion analysis of the p50 subunit revealed that transcriptional activation was mediated by the conserved c-re/-related domain. IKB-P (or a related protein), which binds to the p65 but not the p50 subunit of NF-KB, inhibited stimulation by natural NF-KB but not by recombinant p50. Experiments employing a purified transcription system revealed that efficient induction of transcription by both natural NF-KB or recombinant p50 required a cofactor fraction in addition to the general initiation factors. Combined with DNA-binding experiments, these studies suggest a role of p50 homodimers in transcriptional activation of certain promoters, with a possible preference for those carrying symmetric NF-KB recognition sites, and a potential role of IKB-P in direct transcriptional regulation within the nucleus.