Article

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.

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    • "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. "
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    • "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. "
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    • "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). "
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