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Elife. 2017 Jul 20;6. pii: e27055. doi: 10.7554/eLife.27055.

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

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HIV Dynamics and Replication Program, Center for Cancer Research, National Cancer Institute, Frederick, United States.
Xencor Inc., Monrovia, United States.
Optical Microscopy and Analysis Laboratory, Cancer Research Technology Program, Leidos Biomedical Research, Inc., Frederick, United States.


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.


HIV; RNA; biophysics; infectious disease; microbiology; protein-RNA interaction; retrovirus; structural biology; virus; virus assembly

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