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. 2023 Sep 20;12(18):6079. doi: 10.3390/jcm12186079

Figure 1.

Figure 1

Illustration of SARS-CoV-2 virion structure and replication cycle. The SARS-CoV-2 virion structural protein spike and nucleocapsid are shown in red and yellow colour, respectively, while the genome is shown in blue colour. The positive-sense, single-stranded RNA genome (+ssRNA) is encapsidated in the protein shell. Upon virus entry, the viral genome is released into the cytoplasm. The viral +ssRNA is directly translated by host translational machinery, followed by the synthesis of full-length negative-sense RNA copies for replication and sub-genomic negative-sense RNAs (−sgRNA) to make the positive-sense sub-genomic RNAs (+sgRNAs). The negative-sense RNA synthesis requires a template switch from a body transcription regulatory sequence (TRS-B) to the leader TRS (TRS-L) to generate sub-genomic mRNA. Template switching can take place at any TRS-B in viral genome and co-operatively result in the production of other sub-genomic mRNA species. which acts as templates for the protein synthesis. which is required for viral replication and assembly of viral particles.