An unique mechanism of Coronavirus RNA/protein synthesis

 Coronaviruses are positive sense, single strand RNA viruses, which have unique RNA and protein synthesis system.

 The first half of Coronavirus genome RNA is directly translated by host ribosomes after the viral infection to target cells, which results in the production of a large polyprotein. The polyprotein partially has a protease activity that cleaves itself, which produces many non-structural proteins. The non-structural proteins have RNA dependent RNA polymerase functions, and are involved in viral RNA synthesis.

 The latter half of genome RNA doesn’t encode proteins directly. This area exists as negative sense RNA. The mRNA synthesis of this area occurs after the preceding synthesis of antigenome RNA by using genome RNA as its template. mRNAs, which are also called subgenomic RNA, of these area are synthesized by using the antigenome RNA as the template for mRNA transcription. Then four structural proteins and many accessory proteins are translated from these mRNAs.