title: Human immunodeficiency virus type 1 virion density is not determined by nucleocapsid basic residues.
abstract: The human immunodeficiency virus type 1 (HIV-1) Gag polyprotein is sufficient for assembly and release of virion-like particles from the plasma membrane. To promote assembly, the Gag polyprotein must polymerize to form a shell that lines the inner membrane of nascent virions. Several techniques have been used to functionally map the domain required for Gag polymerization (the I domain). Among these methods, isopycnic centrifugation has been used under the assumption that changes in virion density reflect impairment in Gag-Gag interaction. If virion density is determined by efficient Gag-Gag interaction, then mutation of basic residues in the nucleocapsid (NC) domain should disrupt virion density, since these residues constitute the I domain. However, we have previously shown that simultaneous disruption of up to 10 HIV-1 NC basic residues has no obvious effect on virion density. To rule out the possibility that HIV-1 NC basic residues other than those previously mutated might be important for virion density, mutations were introduced at the remaining sites and the ability of these mutations to affect Gag-Gag interaction and virion density was analyzed. Included in our analysis is a mutant in which all NC basic residues are replaced with alanine. Our results show that disruption of HIV-1 NC basic residues has an enormous effect on Gag-Gag interaction but only a minimal effect on the density of those virions that are still produced. Therefore, the determinants of the I domain and of virion density are genetically distinguishable.
authors.affiliation: Department of Microbiology, College of Physicians and Surgeons, Columbia University, New York, New York 10032, USA.
authors.forename: A
authors.initials: A
authors.lastname: Cimarelli
authors.forename: J
authors.initials: J
authors.lastname: Luban
mesh_terms: D000595:Amino Acid Sequence; D002500:Centrifugation, Isopycnic; D015683:Gene Products, gag / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015497:HIV-1 / Q000235:genetics / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D019169:Jurkat Cells; D008969:Molecular Sequence Data; D009154:Mutation; D019590:Nucleocapsid Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D014771:Virion / Q000502:physiology; D019065:Virus Assembly; D014779:Virus Replication
chemical_list: D015683:Gene Products, gag; D019590:Nucleocapsid Proteins