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]
| Betacoronavirus NS7B protein | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Identifiers | |||||||||
| Symbol | bCoV_NS7B | ||||||||
| Pfam | PF11395 | ||||||||
| InterPro | IPR021532 | ||||||||
| |||||||||
Structure
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
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]
Function
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]