Following entry and reverse transcription, the HIV-1 genome is integrated into the host genome. In contrast to productively infected cells, latently infected cells frequently harbor HIV-1 genomes integrated in heterochromatic structures, allowing persistence of transcriptionally silent proviruses. Microglial cells are the main HIV-1 target cells in the central nervous system and constitute an important reservoir for viral pathogenesis. In the present work, we show that, in microglial cells, the co-repressor COUP-TF interacting protein 2 (CTIP2) recruits a multienzymatic chromatin-modifying complex and establishes a heterochromatic environment at the HIV-1 promoter. We report that CTIP2 recruits histone deacetylase (HDAC)1 and HDAC2 to promote local histone H3 deacetylation at the HIV-1 promoter region. In addition, DNA-bound CTIP2 also associates with the histone methyltransferase SUV39H1, which increases local histone H3 lysine 9 methylation. This allows concomitant recruitment of HP1 proteins to the viral promoter and formation of local heterochromatin, leading to HIV-1 silencing. Altogether, our findings uncover new therapeutic opportunities for purging latent HIV-1 viruses from their cellular reservoirs.

The flagellar regulon of Brucella melitensis 16M contains 31 genes clustered in three loci on the small chromosome. These genes encode a polar sheathed flagellum that is transiently expressed during vegetative growth and required for persistent infection in a mouse model. By following the expression of three flagellar genes (fliF, flgE, and fliC, corresponding to the MS ring, hook, and filament monomer, respectively), we identified a new regulator gene, ftcR (flagellar two-component regulator). Inactivation of ftcR led to a decrease in flagellar gene expression and to impaired Brucella virulence. FtcR has a two-component response regulator domain as well a DNA binding domain and is encoded in the first flagellar locus of B. melitensis. Both the ftcR sequence and its genomic context are conserved in other related ␣-proteobacteria. During vegetative growth in rich medium, ftcR expression showed a peak during the early exponential phase that paralleled fliF gene expression. VjbR, a quorum-sensing regulator of the LuxR family, was previously found to control fliF and flgE gene expression. Here, we provide some new elements suggesting that the effect of VjbR on these flagellar genes is mediated by FtcR. We found that ftcR expression is partially under the control of VjbR and that the expression in trans of ftcR in a vjbR mutant restored the production of the hook protein (FlgE). Finally, FtcR binds directly to the upstream region of the fliF gene. Therefore, our data support the role of FtcR as a flagellar master regulator in B. melitensis and perhaps in other related ␣-proteobacteria.Flagella are highly complex bacterial organelles that are usually well conserved among diverse bacterial species (17,39,46). In addition to motility, the bacterial flagellum is involved in a variety of interactions between the bacterium and its environment (e.g., adhesion, biofilm formation, secretion, and modulation of the host reponse) (7,16,20,22,30,36,42,50,53,57). Flagellar expression involves about 50 flagellar genes, distributed into three or four classes as observed in Escherichia coli (1) and Salmonella enterica serovar Typhimurium (31) or in Caulobacter crescentus (38), Pseudomonas aeruginosa (10), and Vibrio cholerae (41). Complex regulation processes control this hierarchical system, allowing for the expression of the genes of one downstream class if the genes from the upstream class have been expressed.At the top of the flagellar regulatory cascade, one or more distinct master genes encode the transcriptional regulators responsible for turning on and off flagellar synthesis, in response to environmental factors and cell cycle-related signals. In ␥-proteobacteria, this so-called class I is represented by a heterotetrameric complex, FlhD 2 C 2 (lateral flagellar systems), or a sigma 54-associated transcriptional activator of the NtrC family (polar flagellar systems) (4, 52). The situation is somewhat different in ␣-proteobacteria. In C. crescentus, a twocomponent response regulator called CtrA controls a part of the asymmetri...

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Kinetoplastid organisms, such as the protozoan parasite Trypanosoma brucei, compartmentalise several important metabolic pathways in organelles called glycosomes. Glycosomes are related to peroxisomes of yeast and mammalian cells. A subset of glycosomal matrix proteins is routed to the organelles via the peroxisome-targeting signal type 1 (PTS-1). The PEX5 gene homologue has been cloned from T. brucei coding for a protein of the translocation machinery, the PTS-1 receptor. The gene codes for a polypeptide of 654 amino acids with a calculated molecular mass of 70 kDa. Like its homologue in other organisms T. brucei PTS-1 receptor protein (TbPEX5) is a member of the tetratricopeptide repeat (TPR) protein family and contains several copies of the pentapeptide W-X-X-X-F/Y. Northern and Western blot analysis showed that the protein is expressed at different stages of the life cycle of the parasite. The protein has been overproduced in Escherichia coli and purified using immobilized metal affinity chromatography. The purified protein specifically interacts in 6itro with glycosomal phosphoglycerate kinase-C (PGK-C) of T. brucei, a PTS-1 containing protein. The equilibrium dissociation constant (K d ) of PGK-C for purified TbPEX5 is 40 nM. Using biochemical and cytochemical techniques a predominantly cytosolic localization was found for TbPEX5. This is consistent with the idea of receptor cycling between the glycosomes and the cytosol. © 1999 Elsevier Science B.V. All rights reserved. www.elsevier.com/locate/parasitologyAbbre6iations: HK, hexokinase; ORF, open reading frame; PCR, polymerase chain reaction; PEX5, peroxin 5; PGK-C, glycosomal phosphoglycerate kinase; PTS-1, peroxisome-targeting signal type-1; TbPEX5, T. brucei PTS-1 receptor protein; TPR, tetratricopeptide repeat.Note: Nucleotide sequence data reported in this paper are available in the GenBank, EMBL and DDBJ databases under the accession number AF142475.Throughout this paper, the genetic nomenclature as proposed for trypanosomatids has been applied [55], not only for T. brucei, but, in the interest of clarity, also for human and yeasts, although the convention for yeasts is somewhat different (protein: Pex5p instead of PEX5) [56]. * Corresponding author.