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Dissection of specific binding of HIV-1 Gag to the "packaging signal" in viral RNA.

Dissection of specific binding of HIV-1 Gag to the "packaging signal" in viral RNA.
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Comas-Garcia M, Datta SA, Baker L, Varma R, Gudla PR, Rein A,


Comas-Garcia M, Datta SA, Baker L, Varma R, Gudla PR, Rein A, (click to view)

Comas-Garcia M, Datta SA, Baker L, Varma R, Gudla PR, Rein A,

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eLife 2017 07 206() doi 10.7554/eLife.27055

Abstract

Selective packaging of HIV-1 genomic RNA (gRNA) requires the presence of a cis-acting RNA element called the "packaging signal" (Ψ). However, the mechanism by which Ψ promotes selective packaging of the gRNA is not well understood. We used fluorescence correlation spectroscopy and quenching data to monitor the binding of recombinant HIV-1 Gag protein to Cy5-tagged 190-base RNAs. At physiological ionic strength, Gag binds with very similar, nanomolar affinities to both Ψ-containing and control RNAs. We challenged these interactions by adding excess competing tRNA; introducing mutations in Gag; or raising the ionic strength. These modifications all revealed high specificity for Ψ. This specificity is evidently obscured in physiological salt by non-specific, predominantly electrostatic interactions. This nonspecific activity was attenuated by mutations in the MA, CA, and NC domains, including CA mutations disrupting Gag-Gag interaction. We propose that gRNA is selectively packaged because binding to Ψ nucleates virion assembly with particular efficiency.

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