title: Determining the frequency and mechanisms of HIV-1 and HIV-2 RNA copackaging by single-virion analysis.
abstract: HIV-1 and HIV-2 are derived from two distinct primate viruses and share only limited sequence identity. Despite this, HIV-1 and HIV-2 Gag polyproteins can coassemble into the same particle and their genomes can undergo recombination, albeit at an extremely low frequency, implying that HIV-1 and HIV-2 RNA can be copackaged into the same particle. To determine the frequency of HIV-1 and HIV-2 RNA copackaging and to dissect the mechanisms that allow the heterologous RNA copackaging, we directly visualized the RNA content of each particle by using RNA-binding proteins tagged with fluorescent proteins to label the viral genomes. We found that when HIV-1 and HIV-2 RNA are present in viral particles at similar ratios, ∼10% of the viral particles encapsidate both HIV-1 and HIV-2 RNAs. Furthermore, heterologous RNA copackaging can be promoted by mutating the 6-nucleotide (6-nt) dimer initiation signal (DIS) to discourage RNA homodimerization or to encourage RNA heterodimerization, indicating that HIV-1 and HIV-2 RNA can heterodimerize prior to packaging using the DIS sequences. We also observed that the coassembly of HIV-1 and HIV-2 Gag proteins is not required for the heterologous RNA copackaging; HIV-1 Gag proteins are capable of mediating HIV-1 and HIV-2 RNA copackaging. These results define the cis- and trans-acting elements required for and affecting the heterologous RNA copackaging, a prerequisite for the generation of chimeric viruses by recombination, and also shed light on the mechanisms of RNA-Gag recognition essential for RNA encapsidation.
authors.affiliation: HIV Drug Resistance Program, National Cancer Institute, Frederick, MD 21702, USA.
authors.forename: Kari A
authors.initials: KA
authors.lastname: Dilley
authors.forename: Na
authors.initials: N
authors.lastname: Ni
authors.forename: Olga A
authors.initials: OA
authors.lastname: Nikolaitchik
authors.forename: Jianbo
authors.initials: J
authors.lastname: Chen
authors.forename: Andrea
authors.initials: A
authors.lastname: Galli
authors.forename: Wei-Shau
authors.initials: WS
authors.lastname: Hu
mesh_terms: D019281:Dimerization; D015497:HIV-1 / Q000502:physiology*; D012367:RNA, Viral / Q000032:analysis*; D013194:Staining and Labeling / Q000379:methods; D014771:Virion / Q000737:chemistry*; D019065:Virus Assembly; D054301:gag Gene Products, Human Immunodeficiency Virus / Q000378:metabolism
chemical_list: D012367:RNA, Viral; D054301:gag Gene Products, Human Immunodeficiency Virus