Involvement of 5′ and 3′ UTRs in SARS-CoV-2 Virus-like Particle Genome Packaging

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The molecular mechanisms governing the efficient packaging of the large SARS-CoV-2 RNA genome into progeny virions remain incompletely understood, with the role of untranslated regions (UTRs) being particularly enigmatic. Leveraging proximity ligation sequencing data, we identified direct, high-frequency interactions between the viral packaging signal PS9 and both the 5' and 3' UTRs during intracellular replication stages. Functional validation using an infectious virus-like particle (iVLP) system demonstrated that genomes incorporating SARS-CoV-2 UTRs exhibited significantly enhanced packaging efficiency, yielding an increase in both packaged RNA copies and reporter gene expression post-infection. Competitive packaging assays confirmed the UTRs confer a selective advantage during particle assembly. Mechanistically, Western blot and digital Western analysis revealed that UTR-containing iVLPs incorporated approximately 2-fold more nucleocapsid (N) proteins, suggesting enhanced N recruitment or retention. The deletion of specific core sequences within the UTRs predicted to form a base pair with PS9 abrogated this enhancement, suggesting the functional significance of the UTR-PS9 interaction interface. Collectively, these results establish that the 5' and 3' UTRs act synergistically through direct RNA-RNA interactions with PS9 to promote N protein recruitment and enhance packaging efficiency in a PS9-dependent iVLPs system. This UTR-PS9 regulatory axis presents a novel target for therapeutic intervention against SARS-CoV-2 and related coronaviruses.

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