Coronaviruses are enveloped viruses with a positive-sense RNA genome and with a nucleocapsid of helical symmetry. Coronavirus nucleoproteins localize to the cytoplasm and the nucleolus, a subnuclear structure, in both virus-infected primary cells and in cells transfected with plasmids that express N protein. The coronavirus N protein is required for coronavirus RNA synthesis and has RNA chaperone activity that may be involved in template switch. Nucleocapsid protein is the most abundant protein of coronavirus. During virion assembly, N protein binds to viral RNA and leads to the formation of the helical nucleocapsid. Nucleocapsid protein is a highly immunogenic phosphoprotein also implicated in viral genome replication and in modulating cell signaling pathways. Because of the conservation of the N protein sequence and its strong immunogenicity, the N protein of coronavirus is chosen as a diagnostic tool.
Coronavirus N protein is required for coronavirus RNA synthesis, and has RNA chaperone activity that may be involved in template switch. Nucleocapsid protein is a most abundant protein of coronavirus. N protein packages the positive strand viral genome RNA into a helical ribonucleocapsid (RNP) and plays a fundamental role during virion assembly through its interactions with the viral genome and membrane protein M. Plays an important role in enhancing the efficiency of subgenomic viral RNA transcription as well as viral replication. Because of the conservation of N protein sequence and its strong immunogenicity, the N protein of coronavirus is chosen as a diagnostic tool.
Nsp10 have shown that it is a 15-kDa protein of unknown function that has been shown to interact with itself, nsp1, and nsp7. It colocalizes with N to sites of viral replication and is essential for replication. It plays a pivotal role in viral transcription by stimulating both nsp14 3'-5' exoribonuclease and nsp16 2'-O-methyltransferase activities. Therefore plays an essential role in viral mRNAs cap methylation. Nsp10 is a critical regulator of coronavirus RNA synthesis and may play an important role in polyprotein processing.
The Severe Acute Respiratory Syndrome (SARS) Coronavirus (CoV) is an enveloped, positive-stranded RNA viruses that can cause a severe respiratory disease. Its genome consists of a ～30 kb linear, non-segmented, capped, polycistronic, polyadenylated RNA molecule, the first two-third of which is directly translated into two large polyproteins. These two polypeptides are processed into 16 non-structural proteins (nsps), forming the replicase complex, which is active in the cytoplasm in close association with cellular membranes. Nsp1 was proved to be able to suppress host gene expression by promoting host mRNA degradation and was involved in cellular chemokine deregulation. This virus evades the host innate immune response in part through the expression of its non-structural protein (nsp) 1, which inhibits both host gene expression and virus- and interferon (IFN)-dependent signaling. Thus, nsp1 is a promising target for drugs, as inhibition of nsp1 would make SARS-CoV more susceptible to the host antiviral defenses.
The positive-stranded RNA genome of the coronaviruses is translated from ORF1 to yield polyproteins that are proteolytically processed into intermediate and mature nonstructural proteins (nsps). SARS-CoV 2 polyproteins incorporate 16 protein domains (nsps). The putative non-structural protein 2 (nsp2) of SARS-CoV plays an important role in viral transcription and replication, and is an attractive target for anti-SARS drug development.
The ～30kb positive-stranded RNA genome of coronaviruses encodes a replication/transcription machinery that is unusually complex and composed of 16 nonstructural proteins (nsps). The four proteins nsp7 to nsp10, which are conserved among all CoVs but have no functional homologs outside of the Coronaviridae, are translated as part of the viral polyproteins pp1a and pp1ab, and the mature proteins are released by the action of the SARS-CoV protease nsp5. Hexadecamer of nsp7 and nsp8 may possess dsRNA-binding activity. SARS-CoV 2 nonstructural protein 7 (nsp7) is of interest for its potential roles in the transcription and replication of the positive-stranded viral RNA genome.
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