The nucleocapsid (N) protein, the core component of the SARS-CoV-2 virus, binds to the 30-kb viral genomic RNA (vgRNA) to form ribonucleoprotein assemblies that are packaged into ~100 nm membrane-enclosed virions. In addition to viral assembly, the N protein performs other functions, including roles in viral mRNA transcription, replication, and immune regulation, making it a key target for developing diagnostics and vaccines. Recent studies show that N protein and RNA undergo phase separation to form a biomolecular condensate that constitutes the viral core. However, how this condensate becomes selectively enveloped by a membrane remains unclear. Here, using a minimal reconstituted system, we demonstrate that N protein-vgRNA condensates are spontaneously enveloped by lipid bilayer membranes, whereas condensates formed by N protein alone or with genomic RNA fragments fail to undergo envelopment and instead adhere to or weakly deform membranes. We show that RNA length tunes the material properties of N protein condensates, with vgRNA imparting enhanced elasticity. We propose a physical model for SARS-CoV-2 maturation in which adhesion between the membrane and the N protein-vgRNA condensate drives membrane bending, while condensate elasticity preserves core geometry. These results identify RNA-dependent material properties as an underlying physical principle for selective SARS-CoV-2 maturation.
Ravindran, R., Guerin, B., Mahmood, A., Leung, S. S. W., Wahba, H. M., Dagenais, P., Baid, K., Shrivastava, S., Bhuinya, A. B., Williams, S., Sandolache, A., Legault, P., Omichinski, J. G., Banerjee, A., Wiseman, P. W., Hendricks, A. G., Michnick, S. W.
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