Figure 1.

Representation of the viral particle of SARS-CoV-2 demonstrating the structural proteins: S (blue), E (brownish orange), M (red), and N (pink). It also details the post-entry stages of the life cycle of the virus. Following the release of the viral RNA genome to the host cell environment, the nonstructural proteins (NSPs) domain is expressed as two polypeptides and eventually produce PL^pro, M^pro (also known as 3CLpro), and RdRp. Initial processing of the two polypeptides is by host proteases and then is propagated by PL^pro and M^pro. The viral RdRp is also responsible for the replication and amplification of the viral genome. The viral RNA and the N structural protein are biosynthesized in the host cell cytoplasm, whereas viral structural proteins S, M, and E are biosynthesized in the endoplasmic reticulum and transported to the Golgi apparatus. The viral RNA–N complex and S, M, and E proteins are assembled in ERGIC. The mature virus is produced by the budding process. The virus is then released by exocytosis. Note: The virus enters via membrane fusion in the endo/lyso-somes which requires proteolytic activation by cathepsins (a) or via fusion at the cell membrane which requires proteolytic activation by TMPRSS2 (b). Furin may also contribute to the entry of the virus, yet its site of action is not fully established. gRNA means genomic RNA and sgRNA means subgenomic RNA.