NF-B represents a family of eukaryotic transcription factors participating in the regulation of various cellular genes involved in the immediate early processes of immune, acute-phase, and inflammatory responses. Cellular localization and consequently the transcriptional activity of NF-B is tightly regulated by its partner I B␣. Here, we show that the p65 subunit of NF-B is acetylated by both p300 and PCAF on lysines 122 and 123. Both HDAC2 and HDAC3 interact with p65, although only HDAC3 was able to deacetylate p65. Acetylation of p65 reduces its ability to bind 〉-DNA. Finally, acetylation of p65 facilitated its removal from DNA and consequently its I 〉␣-mediated export from the nucleus. We propose that acetylation of p65 plays a key role in I 〉␣-mediated attenuation of NF-〉 transcriptional activity which is an important process that restores the latent state in post-induced cells.

HIV-1 transactivator Tat has greatly contributed to our understanding of transcription elongation by RNAPII. We purified HIV-1 Tat-associated factors from HeLa nuclear extract and show that Tat forms two distinct and stable complexes. Tatcom1 consists of the core active P-TEFb, MLL-fusion partners involved in leukemia (AF9, AFF4, AFF1, ENL, and ELL), and PAF1 complex. Importantly, Tatcom1 formation relies on P-TEFb while optimal CDK9 CTD-kinase activity is AF9 dependent. MLL-fusion partners and PAF1 are required for Tat transactivation. Tatcom2 is composed of CDK9, CycT1, and 7SK snRNP lacking HEXIM. Tat remodels 7SK snRNP by interacting directly with 7SK RNA, leading to the formation of a stress-resistant 7SK snRNP particle. Besides the identification of factors required for Tat transactivation and important for P-TEFb function, our data show a coordinated control of RNAPII elongation by different classes of transcription elongation factors associated in a single complex and acting at the same promoter.

The human immunodeficiency virus (HIV) trans- activator protein, Tat, stimulates transcription from the viral long-terminal repeats (LTR) through an RNA hairpin element, trans-activation responsive region (TAR). We and others have shown that trans-activator protein (Tat)-associated histone acetyltransferases (TAHs), p300 and p300/CBP-associating factor (PCAF), assist functionally in the activation of chromosomally integrated HIV-1 LTR. Here, we show that p300 and PCAF also directly acetylate Tat. We defined two sites of acetylation located in different functional domains of Tat. p300 acetylated Lys50 in the TAR RNA binding domain, while PCAF acetylated Lys28 in the activation domain of Tat. In support of a functional role for acetylation in vivo, histone deacetylase inhibitor (trichostatin A) synergized with Tat in transcriptional activation of the HIV-1 LTR. Synergism was TAR-dependent and required the intact presence of both Lys28 and Lys50. Mechanistically, acetylation at Lys28 by PCAF enhanced Tat binding to the Tat-associated kinase, CDK9/P-TEFb, while acetylation by p300 at Lys50 of Tat promoted the dissociation of Tat from TAR RNA that occurs during early transcription elongation. These data suggest that acetylation of Tat regulates two discrete and functionally critical steps in transcription, binding to an RNAP II CTD-kinase and release of Tat from TAR RNA.

HIV‐1 gene expression is the major determinant regulating the rate of virus replication and, consequently, AIDS progression. Following primary infection, most infected cells produce virus. However, a small population becomes latently infected and constitutes the viral reservoir. This stable viral reservoir seriously challenges the hope of complete viral eradication. Viewed in this context, it is critical to define the molecular mechanisms involved in the establishment of transcriptional latency and the reactivation of viral expression. We show that Suv39H1, HP1γ and histone H3Lys9 trimethylation play a major role in chromatin‐mediated repression of integrated HIV‐1 gene expression. Suv39H1, HP1γ and histone H3Lys9 trimethylation are reversibly associated with HIV‐1 in a transcription‐dependent manner. Finally, we show in different cellular models, including PBMCs from HIV‐1‐infected donors, that HIV‐1 reactivation could be achieved after HP1γ RNA interference.