Figure 1.

Genome organization of SARS-CoV and SARS-CoV-2. The upper panel shows the genomic organization of SARS-CoV. It contains two polyproteins pp1a and pp1b synthesized from ORF1a and 1b. These polypeptides undergo a series of proteolytic cleavages to form 16 nonstructural proteins. These 16 nonstructural proteins are encoded by the first two thirds of the genome (figure not drawn to scale). The second one third of the genome encodes for four structural proteins S, E, M, and N. Interspersed within these genes are genes for the expression accessory proteins. SARS-CoV-2, a more recently discovered virus, has genomic organization almost identical to SARS-CoV. Accessory protein 8 for SARS-CoV-2 is not divided into 8a and 8b as in SARS-CoV and two ORF for spike proteins are not present in this virus. In addition, SARS-CoV-2 protein contains accessory protein 10 potentially not present in SARS-CoV.

ORF indicates Open Reading Frames.