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Betacoronavirus NS7B protein
Available protein structures:
Pfam  structures / ECOD  
PDBsumstructure summary

ORF7b is a gene found in coronaviruses of the genus Betacoronavirus, which expresses the accessory protein Betacoronavirus NS7b protein.[1] It is a short, highly hydrophobic transmembrane protein of unknown function.[1][2]


ORF7b protein is a transmembrane protein with a single transmembrane helix whose membrane topology orients the C-terminus in the cytosol.[1] In SARS-CoV, it is 44 amino acid residues and in SARS-CoV-2 it is 43 residues, with about 85% sequence identity.[2]

Expression and localization[edit]

ORF7b is an overlapping gene that overlaps ORF7a.[3] The protein is probably expressed from subgenomic RNA through leaky scanning.[1] In SARS-CoV, it is localized to the Golgi apparatus, which requires the transmembrane helix sequence.[1][4] In SARS-CoV-2, it has been reported to associate with the endoplasmic reticulum.[5]


The function of the ORF7b protein is not well characterized. It is not essential for viral replication,[1][3] though there is inconsistent evidence from studies of SARS-CoV on whether its deletion affects replication.[1][6] In SARS-CoV, it has been identified incorporating into virions, suggesting it is a minor viral structural protein.[1][7] A SARS-CoV-2 variant with a deletion mutation in the ORF7b region, resulting in a fusion protein between ORF7b and ORF8, has been identified, of unclear significance.[2][8]


  1. ^ a b c d e f g h Liu DX, Fung TS, Chong KK, Shukla A, Hilgenfeld R (September 2014). "Accessory proteins of SARS-CoV and other coronaviruses". Antiviral Research. 109: 97–109. doi:10.1016/j.antiviral.2014.06.013. PMC 7113789. PMID 24995382.
  2. ^ a b c Redondo N, Zaldívar-López S, Garrido JJ, Montoya M (7 July 2021). "SARS-CoV-2 Accessory Proteins in Viral Pathogenesis: Knowns and Unknowns". Frontiers in Immunology. 12: 708264. doi:10.3389/fimmu.2021.708264. hdl:10261/249329. PMC 8293742. PMID 34305949.
  3. ^ a b Pekosz A, Schaecher SR, Diamond MS, Fremont DH, Sims AC, Baric RS (2006). "Structure, Expression, and Intracellular Localization of the SARS-CoV Accessory Proteins 7a and 7b". The Nidoviruses. Advances in Experimental Medicine and Biology. Vol. 581. pp. 115–120. doi:10.1007/978-0-387-33012-9_20. ISBN 978-0-387-26202-4. PMC 7123408. PMID 17037516.
  4. ^ Schaecher SR, Diamond MS, Pekosz A (October 2008). "The transmembrane domain of the severe acute respiratory syndrome coronavirus ORF7b protein is necessary and sufficient for its retention in the Golgi complex". Journal of Virology. 82 (19): 9477–9491. doi:10.1128/JVI.00784-08. PMC 2546951. PMID 18632859.
  5. ^ Zhang J, Cruz-Cosme R, Zhuang MW, Liu D, Liu Y, Teng S, et al. (November 2020). "A systemic and molecular study of subcellular localization of SARS-CoV-2 proteins". Signal Transduction and Targeted Therapy. 5 (1): 269. doi:10.1038/s41392-020-00372-8. PMC 7670843. PMID 33203855.
  6. ^ McBride R, Fielding BC (November 2012). "The role of severe acute respiratory syndrome (SARS)-coronavirus accessory proteins in virus pathogenesis". Viruses. 4 (11): 2902–2923. doi:10.3390/v4112902. PMC 3509677. PMID 23202509.
  7. ^ Schaecher SR, Mackenzie JM, Pekosz A (January 2007). "The ORF7b protein of severe acute respiratory syndrome coronavirus (SARS-CoV) is expressed in virus-infected cells and incorporated into SARS-CoV particles". Journal of Virology. 81 (2): 718–731. doi:10.1128/JVI.01691-06. PMC 1797472. PMID 17079322.
  8. ^ Su YC, Anderson DE, Young BE, Linster M, Zhu F, Jayakumar J, et al. (July 2020). "Discovery and Genomic Characterization of a 382-Nucleotide Deletion in ORF7b and ORF8 during the Early Evolution of SARS-CoV-2". mBio. 11 (4). doi:10.1128/mBio.01610-20. hdl:11343/277716. PMC 7374062. PMID 32694143.