Barrier-to-autointegration factor BAF binds p55 Gag and matrix and is a host component of human immunodeficiency virus type 1 virions.

Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Journal of Virology (Impact Factor: 4.65). 01/2004; 77(24):13084-92. DOI: 10.1128/JVI.77.24.13084-13092.2003
Source: PubMed

ABSTRACT Barrier-to-autointegration factor (BAF) is a conserved human chromatin protein exploited by retroviruses. Previous investigators showed that BAF binds double-stranded DNA nonspecifically and is a host component of preintegration complexes (PICs) isolated from cells infected with human immunodeficiency virus type 1 (HIV-1) or Moloney murine leukemia virus. BAF protects PIC structure and stimulates the integration of salt-stripped PICs into target DNA in vitro. PICs are thought to acquire BAF from the cytoplasm during infection. However, we identified two human tissues (of 16 tested) in which BAF mRNA was not detected: thymus and peripheral blood leukocytes, which are enriched in CD4(+) T lymphocytes and macrophage precursors, respectively. BAF protein was detected in activated but not resting CD4(+) T lymphocytes; thus, if BAF were essential for PIC function, we hypothesized that virions might "bring their own BAF." Supporting this model, BAF copurified with HIV-1 virions that were digested with subtilisin to remove microvesicle contaminants, and BAF was present in approximately zero to three copies per virion. In three independent assays, BAF bound directly to both p55 Gag (the structural precursor of HIV-1 virions) and its cleaved product, matrix. Using lysates from cells overexpressing Gag, endogenous BAF and Gag were coimmunoprecipitated by antibodies against Gag. Purified recombinant BAF had low micromolar affinities (1.1 to 1.4 micro M) for recombinant Gag and matrix. We conclude that BAF is present at low levels in incoming virions, in addition to being acquired from the cytoplasm of newly infected cells. We further conclude that BAF might contribute to the assembly or activity of HIV-1 PICs through direct binding to matrix, as well as DNA.

Download full-text


Available from: Katherine L Wilson, Jul 14, 2015
  • Source
    • "Indeed, the elucidation that the RNA helicase RIG-I can act as a cytoplasmic RNA sensor, and indeed can trigger the downstream activation of host response genes indicates that this is true (Meylan and Tschopp, 2006). Because BAF is a highly conserved protein (Figure S4) found in all eukaryotic dividing cells that have been tested (Mansharamani et al., 2003) and because it binds DNA avidly and without regard to sequence specificity , our findings raise the possibility that BAF might be a central component of a widespread host defense which recognizes and silences foreign DNA. It will be of significant interest to determine whether, subsequent to its binding to foreign DNA, BAF may function like RIG-I and contribute to a signaling cascade that alerts cells of a possible infection. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Barrier to autointegration factor (BAF) is a DNA-binding protein found in the nucleus and cytoplasm of eukaryotic cells that functions to establish nuclear architecture during mitosis. Herein, we demonstrate a cytoplasmic role for BAF in host defense during poxviral infections. Vaccinia is the prototypic poxvirus, a family of DNA viruses that replicate exclusively in the cytoplasm of infected cells. Mutations in the vaccinia B1 kinase (B1) compromise viral DNA replication, but the mechanism by which B1 achieves this has remained elusive. We now show that BAF acts as a potent inhibitor of poxvirus replication unless its DNA-binding activity is blocked by B1-mediated phosphorylation. These data position BAF as the effector of an innate immune response that prevents replication of exogenous viral DNA in the cytoplasm. To enable the virus to evade this defense, the poxviral B1 has evolved to usurp a signaling pathway employed by the host cell.
    Cell host & microbe 06/2007; 1(3):187-97. DOI:10.1016/j.chom.2007.03.007 · 12.19 Impact Factor
  • Source
    • "Potential HIV-1 integration co-factors can be divided into two groups based on whether they interact directly with IN. Some, like the barrier-to-autointegration factor (BAF) and high mobility group protein A1 (HMGA1), appear to associate with PICs primarily through their affinities for DNA (Harris and Engelman, 2000; Hindmarsh et al., 1999; Li et al., 2000; Mansharamani et al., 2003). Others, such as IN-interactor 1 (Kalpana et al., 1994), lens epithelium-derived growth factor (LEDGF)/p75 (Cherepanov et al., 2003; Emiliani et al., 2005; Turlure et al., 2004), hepatoma-derived growth factor related protein 2 (HRP2) (Cherepanov et al., 2004), and histone acetyltransferase p300 (Cereseto et al., 2005), bind directly to IN. LEDGF/p75 appears to be the dominant cellular binding partner of HIV-1 IN. "
    [Show abstract] [Hide abstract]
    ABSTRACT: LEDGF/p75 binding-defective IN mutant viruses were previously characterized as replication-defective, yet RNAi did not reveal an essential role for the host factor in HIV-1 replication. Correlative analyses of protein binding and viral fitness were expanded here by targeting 12 residues at the IN-LEDGF/p75 binding interface. Whereas many of the resultant viruses were defective, the majority of the INs displayed wild-type in vitro integration activities. Though an overall trend of parallel loss of LEDGF/p75 binding and HIV-1 infectivity was observed, a strict correlation was not. His-tagged IN(A128Q), derived from a phenotypically wild-type virus, failed to pull-down LEDGF/p75, but IN(A128Q) was effectively recovered in a reciprocal GST pull-down assay. Under these conditions, IN(H171A), also derived from a phenotypically wild-type virus, interacted less efficiently than a previously described interaction-defective mutant, IN(Q168A). Thus, the relative affinity of the in vitro IN-LEDGF/p75 interaction is not a universal predictor of IN mutant viral fitness.
    Virology 02/2007; 357(1):79-90. DOI:10.1016/j.virol.2006.08.011 · 3.28 Impact Factor
  • Source
    • "munodeficiency virus type 1 (Lee and Craigie, 1998; Harris and Engelman, 2000; Lin and Engelman, 2003). BAF binds directly to the human immunodeficiency virus (HIV)-1-en- coded matrix protein (Mansharamani et al., 2003). Both BAF and LAP2␣, a soluble LEM-domain protein, are present in DNA-containing retroviral preintegration complexes (Mansharamani et al., 2003; Suzuki et al., 2004), and BAF is required for these complexes to integrate into target DNA in vitro (Suzuki et al., 2004, and references therein). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Barrier-to-autointegration factor (BAF) is a conserved 10-kDa chromatin protein essential in proliferating cells. BAF dimers bind double-stranded DNA, histone H3, histone H1.1, lamin A, and transcription regulators, plus emerin and other LEM-domain nuclear proteins. Two-dimensional gel analysis showed that endogenous human and Xenopus BAF are posttranslationally modified by phosphorylation and potentially other modifications and that they are hyperphosphorylated during mitosis. The invariant Ser-4 residue on BAF is a major site of phosphorylation during both interphase and mitosis. In HeLa cells that overexpressed the phosphomimetic BAF missense mutant S4E, but not S4A, emerin mislocalized from the nuclear envelope, suggesting Ser-4-nonphosphorylated BAF normally promotes emerin localization at the nuclear envelope. Supporting this model, wild-type BAF but not mutant S4E enhanced emerin binding to lamin A in vitro. Thus, Ser-4-unphosphorylated BAF has a positive role in localizing emerin; this role may be disease relevant because loss or mislocalization of emerin causes Emery-Dreifuss muscular dystrophy. Our findings further suggest Ser-4 phosphorylation inhibits BAF binding to emerin and lamin A, and thereby weakens emerin-lamin interactions during both mitosis and interphase.
    Molecular Biology of the Cell 04/2006; 17(3):1154-63. DOI:10.1091/mbc.E05-04-0356 · 4.55 Impact Factor
Show more