Coronavirus genome packaging and nucleocapsid assembly

Coronaviruses are a family of positive-strand RNA viruses that exhibit highly selective packaging of their genomic RNA (gRNA) into assembled virions, despite the presence of a large excess of subgenomic viral RNA species and host RNA in infected cells. While this high selectivity is critical to evading host innate immune responses, surprisingly, it is not essential for virion assembly. This review focuses on four main topics: (i) coronavirus genome packaging signals (PSs)-how they are found and the function they serve; (ii) the viral components that recognize the PS in order to bring about selective gRNA packaging; (iii) coronavirus nucleocapsid structure and assembly; and (iv) the relationship between nucleocapsid protein phosphorylation and nucleocapsid assembly versus RNA synthesis. Current understanding of these areas has benefited immensely from advances made by recent studies, most of which were performed in response to the emergence of the coronavirus responsible for the COVID-19 pandemic. Throughout this review, emphasis is placed on the counterintuitive distinction between coronavirus selective gRNA packaging and nucleocapsid assembly.