title: Elements in HIV-1 Gag contributing to virus particle assembly.
abstract: The Gag polyprotein is the building block of retroviral particles and its expression is sufficient for assembly in cells. In HIV-1, nucleic acid (NA) is required for recombinant Gag molecules to assemble in a defined system in vitro. Experiments performed by Barklis and co-workers suggested that NA contributes to assembly by promoting Gag oligomerization. Gag is composed of four main domains: the matrix (MA), capsid (CA), nucleocapsid (NC), and p6 domains. We have recently shown that the SP1 linker, which lies between the CA and NC domains, assumes a helical structure at high, but not low, concentrations. We suggested that Gag oligomerization mediates assembly via an SP1-dependent conformational switch that exposes new interfaces for assembly. Although NA is required for assembly in vitro, deletion of NC, the main RNA-binding domain, does not eliminate particle formation in vivo; these particles lack NA. We hypothesized that alternative pathways that lead to Gag oligomerization or an increase in local Gag concentration, namely Gag-membrane or inter-protein interactions, rescue assembly in the absence of NC-RNA binding. We constructed mutants in which either Gag-membrane binding, the Gag dimer interface, or NC-RNA binding are disrupted. None of these mutants disables assembly. However, combined mutations in any two of these three classes render Gag completely unable to form virus-like particles. Thus, it seems, Gag utilizes at least three types of interactions to form oligomers and any two out of the three are sufficient for assembly.
authors.affiliation: HIV Drug Resistance Program, National Cancer Institute, Frederick National Laboratory for Cancer Research, Frederick, MD 21702, USA.
authors.forename: Ina P
authors.initials: IP
authors.lastname: O'Carroll
authors.forename: Ferri
authors.initials: F
authors.lastname: Soheilian
authors.forename: Anne
authors.initials: A
authors.lastname: Kamata
authors.forename: Kunio
authors.initials: K
authors.lastname: Nagashima
authors.forename: Alan
authors.initials: A
authors.lastname: Rein
mesh_terms: D015658:HIV Infections / Q000821:virology*; D015497:HIV-1 / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D006801:Humans; D011485:Protein Binding; D012367:RNA, Viral / Q000235:genetics / Q000378:metabolism; D019065:Virus Assembly; D054301:gag Gene Products, Human Immunodeficiency Virus / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D012367:RNA, Viral; D054301:gag Gene Products, Human Immunodeficiency Virus