Distinct binding interactions of HIV-1 Gag to Psi and non-Psi RNAs: Implications for viral genomic RNA packaging

Joseph A. Webb, Christopher P. Jones, Leslie J. Parent, Ioulia Rouzina, Karin Musier-Forsyth

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69 Scopus citations


Despite the vast excess of cellular RNAs, precisely two copies of viral genomic RNA (gRNA) are selectively packaged into new human immunodeficiency type 1 (HIV-1) particles via specific interactions between the HIV-1 Gag and the gRNA psi (Ψ) packaging signal. Gag consists of the matrix (MA), capsid, nucleocapsid (NC), and p6 domains. Binding of the Gag NC domain to Ψ is necessary for gRNA packaging, but the mechanism by which Gag selectively interacts with Ψ is unclear. Here, we investigate the binding of NC and Gag variants to an RNA derived from Ψ (Psi RNA), as well as to a non-Ψ region (TARPolyA). Binding was measured as a function of salt to obtain the effective charge (Zeff) and nonelectrostatic (i.e., specific) component of binding, Kd(1M). Gag binds to Psi RNA with a dramatically reduced Kd(1M) and lower Zeff relative to TARPolyA. NC, GagΔMA, and a dimerization mutant of Gag bind TARPolyA with reduced Zeff relative to WT Gag. Mutations involving the NC zinc finger motifs of Gag or changes to the G-rich NC-binding regions of Psi RNA significantly reduce the nonelectrostatic component of binding, leading to an increase in Zeff. These results show that Gag interacts with gRNA using different binding modes; both the NC and MA domains are bound to RNA in the case of TARPolyA, whereas binding to Psi RNA involves only the NC domain. Taken together, these results suggest a novel mechanism for selective gRNA encapsidation.

Original languageEnglish (US)
Pages (from-to)1078-1088
Number of pages11
Issue number8
StatePublished - Aug 2013

All Science Journal Classification (ASJC) codes

  • Molecular Biology


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