Fig. 4 Life cycle of highly pathogenic human CoVs. These CoVs enter host cells by first binding to their respective cellular receptors via the surface S protein. Viral genomic RNA is released and translated into viral polymerase proteins. Viral RNA and nucleocapsid (N) structural protein are replicated, transcribed, or synthesized in the cytoplasm, whereas other viral structural proteins, including S, membrane (M), and envelope (E), are transcribed then translated in the endoplasmic reticulum (ER) and transported to the Golgi. The viral RNA–N complex and S, M, and E proteins are further assembled in the ER–Golgi intermediate compartment (ERGIC) to form a mature virion, then released from host cells [62].