Let's phase it: viruses are master architects of biomolecular condensates.

Viruses compartmentalize their replication and assembly machinery to both evade detection and concentrate the viral proteins and nucleic acids necessary for genome replication and virion production. Accumulating evidence suggests that diverse RNA and DNA viruses form replication organelles and nucleocapsid assembly sites using phase separation. In general, the biogenesis of these compartments is regulated by two types of viral protein, collectively known as antiterminators and nucleocapsid proteins, respectively. Herein, we discuss how RNA viruses establish replication organelles and nucleocapsid assembly sites, and the evidence that these compartments form through phase separation. While this review focuses on RNA viruses, accumulating evidence suggests that all viruses rely on phase separation and form biomolecular condensates important for completing the infectious cycle. Recent insights from biophysics have revealed that viruses harness phase separation to mediate replication organelle biogenesis and nucleocapsid assembly. Replication organelle biogenesis is mediated by viral antiterminator proteins (sometimes with the aid of an additional phosphoprotein), which bind to, and condense, the viral RNA. Nucleocapsid assembly is mediated by nucleocapsid proteins, which bind to, and condense, the viral RNA within the virion. Across RNA viruses, the phosphoprotein, antiterminator, and nucleocapsid activities may be provided by a single modular protein or several distinct viral proteins. Collaborations between virologists and biophysicists promise to accelerate discovery in both fields. [ABSTRACT FROM AUTHOR]