title: HIV-2 genome dimerization is required for the correct processing of Gag: a second-site reversion in matrix can restore both processes in dimerization-impaired mutant viruses.
abstract: A unique feature of retroviruses is the packaging of two copies of their genome, noncovalently linked at their 5' ends. In vitro, dimerization of human immunodeficiency virus type 2 (HIV-2) RNA occurs by interaction of a self-complementary sequence exposed in the loop of stem-loop 1 (SL-1), also termed the dimer initiation site (DIS). However, in virions, HIV-2 genome dimerization does not depend on the DIS. Instead, a palindrome located within the packaging signal (Psi) is the essential motif for genome dimerization. We reported previously that a mutation within Psi decreasing genome dimerization and packaging also resulted in a reduced proportion of mature particles (A. L'Hernault, J. S. Greatorex, R. A. Crowther, and A. M. Lever, Retrovirology 4:90, 2007). In this study, we investigated further the relationship between HIV-2 genome dimerization, particle maturation, and infectivity by using a series of targeted mutations in SL-1. Our results show that disruption of a purine-rich ((392)-GGAG-(395)) motif within Psi causes a severe reduction in genome dimerization and a replication defect. Maintaining the extended SL-1 structure in combination with the (392)-GGAG-(395) motif enhanced packaging. Unlike that of HIV-1, which can replicate despite mutation of the DIS, HIV-2 replication depends critically on genome dimerization rather than just packaging efficiency. Gag processing was altered in the HIV-2 dimerization mutants, resulting in the accumulation of the MA-CA-p2 processing intermediate and suggesting a link between genome dimerization and particle assembly. Analysis of revertant SL-1 mutant viruses revealed that a compensatory mutation in matrix (70TI) could rescue viral replication and partially restore genome dimerization and Gag processing. Our results are consistent with interdependence between HIV-2 RNA dimerization and the correct proteolytic cleavage of the Gag polyprotein.
authors.affiliation: Department of Medicine, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Anne
authors.initials: A
authors.lastname: L'Hernault
authors.forename: Eva U
authors.initials: EU
authors.lastname: Weiss
authors.forename: Jane S
authors.initials: JS
authors.lastname: Greatorex
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Lever
mesh_terms: D020816:Amino Acid Motifs; D002460:Cell Line; D019281:Dimerization; D016679:Genome, Viral; D015658:HIV Infections / Q000821:virology*; D015498:HIV-2 / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D006801:Humans; D055029:Inverted Repeat Sequences; D008969:Molecular Sequence Data; D009154:Mutation; D009690:Nucleic Acid Conformation; D011499:Protein Processing, Post-Translational; D014779:Virus Replication; D054301:gag Gene Products, Human Immunodeficiency Virus / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D054301:gag Gene Products, Human Immunodeficiency Virus