Molecular mechanisms of simian immunodeficiency virus SIVagm RNA encapsidation

Primate lentiviruses are composed of several distinct lineages, including human immunodeficiency virus type 1 (HIV-1), HIV-2, and simian immunodeficiency virus SIVagm. HIV-1 and HIV-2 have significant differences in the mechanisms of viral RNA encapsidation. Therefore, the RNA packaging mechanisms of SIVagm cannot be predicted from the studies of HIV-1 and HIV-2. We examined the roles of the nucleocapsid (NC) zinc finger motifs on RNA packaging by mutating the conserved zinc finger (CCHC) motifs, and whether SIVagm has a preference to package RNA in cis by comparing the RNA packaging efficiencies of gag mutants in the presence of a wild-type vector. Our results indicate that the SIVagm NC domain plays an important role in Gag–RNA recognition; furthermore SIVagm is distinct from the other currently known primate lentiviruses as destroying either zinc finger motif in the NC causes very drastic RNA packaging defects. Additionally, trans-packaging is a major mechanism for SIVagm RNA encapsidation.