Subcellular Localization of SARS-CoV Structural Proteins

Abstract

Coronaviruses are enveloped viruses that assemble at intracellular membranes of the endoplasmic reticulum–Golgi intermediate compartment (ERGIC) in infected cells.1 S and M are the main components of the viral envelope. The E protein is a minor component of the envelope, but plays an important role in virus assembly.2 Coronavirus envelope formation is nucleocapsid independent. Expression of only the E and M proteins is sufficient for the formation of virus-like-particles (VLPs) of many coronaviruses.3–5 The N protein is a multifunctional phosphoprotein that encapsidates the viral genome and plays a role in virus assembly.6, 7 N also appears to be involved in viral RNA replication and/or transcription.8, 9 The aim in this study was to provide a comprehensive view of the subcellular localization of the main SARS-CoV structural proteins. The S, M, E, and N genes were expressed in BHK-21 cells, and localization of the proteins was analyzed by indirect immunofluorescence microscopy. The proteins were co-analyzed with specific organelle markers for the endoplasmic reticulum (ER) and Golgi. Additionally, the M and E proteins were co-localized with a cellular marker for the ERGIC. The N protein remained cytoplasmic. The S, M, and E proteins were found to concentrate to the Golgi region, although some S appeared to also be transported to the cell surface.