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. 2021 Jul 14;12:682603. doi: 10.3389/fmicb.2021.682603

FIGURE 1.

FIGURE 1

The genomes of alpha-CoVs (HCoV-229E, HCoV-NL63), beta-Covs (MHV, HCoV-OC43, HCoV-HKU1, Bat-SL-RaTG13, SARS-CoV-1, MERS-CoV and SARS-CoV-2), delta-Covs (IBV), and gamma-CoVs (PDCoV). Coronaviruses contain a positive-sense, single-stranded RNA [ssRNA (+)] genome of 27–32 kb. The 5′-terminal two thirds of the genome encode a polyprotein pp1a and pp1b which are further cleaved into 16 nps that are involved in genome transcription and replication. The 3′ terminus encodes structural proteins: envelope glycoprotein (S), envelope (E), membrane (M), and nucleocapsid (N). In addition, accessory genes species-specific are interspersed or embedded as an alternative ORF within another genes (the ORF I gene of MHV, the Ia and Ib gene). The SARS-CoV-1 (SARS-CoV-1 reference sequence AY274119) possess 9 ORFs (ORF3a, 3b, 6, 7a, 7b, 8a, 8b, 9b, and 9c), the MERS (MERS-CoV reference sequence NC_019843) retains 6 ORFS (ORF3, 4a, 4b, 5, 8b, and 8c), and the SARS-CoV-2 (SARS-CoV-2 reference sequence NC_045512) has 11 ORFS (ORF3a, 3b, 3c, 3d, 6, 7a, 7b, 8, 9b, 9c, and 10).