title: NC-mediated nucleolar localization of retroviral gag proteins.
abstract: The assembly and release of retrovirus particles from the cell membrane is directed by the Gag polyprotein. The Gag protein of Rous sarcoma virus (RSV) traffics through the nucleus prior to plasma membrane localization. We previously reported that nuclear localization of RSV Gag is linked to efficient packaging of viral genomic RNA, however the intranuclear activities of RSV Gag are not well understood. To gain insight into the properties of the RSV Gag protein within the nucleus, we examined the subnuclear localization and dynamic trafficking of RSV Gag. Restriction of RSV Gag to the nucleus by mutating its nuclear export signal (NES) in the p10 domain or interfering with CRM1-mediated nuclear export of Gag by leptomycin B (LMB) treatment led to the accumulation of Gag in nucleoli and discrete nucleoplasmic foci. Retention of RSV Gag in nucleoli was reduced with cis-expression of the 5' untranslated RU5 region of the viral RNA genome, suggesting the psi (Ψ) packaging signal may alter the subnuclear localization of Gag. Fluorescence recovery after photobleaching (FRAP) demonstrated that the nucleolar fraction of Gag was highly mobile, indicating that there was rapid exchange with Gag proteins in the nucleoplasm. RSV Gag is targeted to nucleoli by a nucleolar localization signal (NoLS) in the NC domain, and similarly, the human immunodeficiency virus type 1 (HIV-1) NC protein also contains an NoLS consisting of basic residues. Interestingly, co-expression of HIV-1 NC or Rev with HIV-1 Gag resulted in accumulation of Gag in nucleoli. Moreover, a subpopulation of HIV-1 Gag was detected in the nucleoli of HeLa cells stably expressing the entire HIV-1 genome in a Rev-dependent fashion. These findings suggest that the RSV and HIV-1 Gag proteins undergo nucleolar trafficking in the setting of viral infection.
authors.affiliation: Department of Medicine, Penn State College of Medicine, 500 University Drive, Hershey, PA 17033, USA.
authors.forename: Timothy L
authors.initials: TL
authors.lastname: Lochmann
authors.forename: Darrin V
authors.initials: DV
authors.lastname: Bann
authors.forename: Eileen P
authors.initials: EP
authors.lastname: Ryan
authors.forename: Andrea R
authors.initials: AR
authors.lastname: Beyer
authors.forename: Annie
authors.initials: A
authors.lastname: Mao
authors.forename: Alan
authors.initials: A
authors.lastname: Cochrane
authors.forename: Leslie J
authors.initials: LJ
authors.lastname: Parent
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D002466:Cell Nucleolus / Q000378:metabolism / Q000821:virology*; D015967:Gene Expression Regulation, Viral; D015683:Gene Products, gag / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015658:HIV Infections / Q000378:metabolism / Q000821:virology*; D015497:HIV-1 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals; D021381:Protein Transport; D011784:Quail; D052736:Rous sarcoma virus / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001357:Sarcoma, Avian / Q000378:metabolism / Q000821:virology*; D016415:Sequence Alignment; D054301:gag Gene Products, Human Immunodeficiency Virus / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D015683:Gene Products, gag; D019913:Nuclear Localization Signals; D054301:gag Gene Products, Human Immunodeficiency Virus