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Fig. 2 | Stem Cell Research & Therapy

Fig. 2

From: Spotlight on therapeutic efficiency of mesenchymal stem cells in viral infections with a focus on COVID-19

Fig. 2

SARS-CoV-2 replication. SARS-CoV-2 S protein connects to ACE2 receptor to membrane fusion and discharges the viral genome into the host cell cytoplasm. After the entering the virus, the viral RNA is uncovered in the cytoplasm. ORF1a and ORF1ab are translated to produce pp1a and pp1ab that undergo further cleavage into smaller proteins containing RNA-dependent RNA polymerase, helicase, and nonstructural protein. RNA replicase–transcriptase complex (RTC) localizes to altered intracellular membranes isolated from the rough endoplasmic reticulum (ER) in the perinuclear area, where it generates (−) RNAs. Throughout replication, complete (−)RNA transcripts of the genome are generated and used as patterns for full (+) RNA genomes. Throughout transcription, a member of subgenomic RNAs (sg-RNA), containing those encoding S, M, E, and E protein, is generated by intermittent transcription. In this procedure, a nested set of (−)sg-RNA is generated that modify in length at the 3′ end and 5′-leader sequence, which is essential for translation. Then, this (−) sg-RNA are transcribed into (+) sg-mRNAs. Afterward, S, M, E, and N proteins are gathered in the nucleocapsid and viral envelope at the ER–Golgi intermediate compartment (ERGIC), then through exocytosis of SARS-CoV-2, released to vesicles [129,130,131]

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