Viruses, Volume 12, Issue 5
May 2020 - 98 articles
Cover Story: HIV-1 retroviral nucleocapsid (NC) proteins facilitate the rearrangement of nucleic acid secondary structures during reverse transcription, allowing the transactivation response (TAR) RNA hairpin to be transiently destabilized and annealed to a complementary DNA hairpin. Yet during viral assembly, NC, as a domain of the group-specific antigen (Gag) polyprotein, binds genomic RNA and facilitates packaging into new virions. So how can the same protein, alone or as part of Gag, perform such different RNA binding functions in the viral life cycle? Combining single-molecule optical tweezers measurements with a quantitative mfold-based model, we characterize the stability and unfolding barrier for TAR RNA. While both NCp7 and Gagp6 destabilize the TAR hairpin, only NCp7 destabilizes the top loop, shifting the barrier location toward the folded state and increasing the natural rate of hairpin opening by 104. These results explain why Gag cleavage and NC release is an essential prerequisite
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