title: Barrier-to-autointegration factor BAF binds p55 Gag and matrix and is a host component of human immunodeficiency virus type 1 virions.
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.
authors.affiliation: Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
authors.forename: Malini
authors.initials: M
authors.lastname: Mansharamani
authors.forename: David R M
authors.initials: DR
authors.lastname: Graham
authors.forename: Daphne
authors.initials: D
authors.lastname: Monie
authors.forename: Kenneth K
authors.initials: KK
authors.lastname: Lee
authors.forename: James E K
authors.initials: JE
authors.lastname: Hildreth
authors.forename: Robert F
authors.initials: RF
authors.lastname: Siliciano
authors.forename: Katherine L
authors.initials: KL
authors.lastname: Wilson
mesh_terms: D015496:CD4-Positive T-Lymphocytes / Q000276:immunology / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015683:Gene Products, gag / Q000235:genetics / Q000378:metabolism*; D015488:HIV Antigens / Q000378:metabolism*; D015497:HIV-1 / Q000378:metabolism* / Q000472:pathogenicity; D006367:HeLa Cells; D006801:Humans; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism*; D014764:Viral Proteins; D014771:Virion / Q000378:metabolism*; D016662:Virus Integration; D054301:gag Gene Products, Human Immunodeficiency Virus
chemical_list: C501959:BANF1 protein, human; D004268:DNA-Binding Proteins; D015683:Gene Products, gag; D015488:HIV Antigens; D009687:Nuclear Proteins; D011498:Protein Precursors; D014764:Viral Proteins; D054301:gag Gene Products, Human Immunodeficiency Virus; C054858:p17 protein, Human Immunodeficiency Virus Type 1; C059767:p55 gag precursor protein, Human immunodeficiency virus 1