Article
Characterization of a unique group-specific protein (U122) of the severe acute respiratory syndrome (SARS) coronavirus
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Published: | May 26, 2004 |
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A novel coronavirus (CoV) has been identified as the etiological agent of severe acute respiratory syndrome (SARS). The SARS-CoV genome encodes the characteristic essential coronavirus replication and structural proteins. Additionally, the genome contains six group-specific open reading frames (ORFs) larger than 50 amino acids, with no known homologues. As with the group-specific genes of the other coronaviruses, little is known about the SARS-CoV group-specific genes. SARS-CoV ORF7a encodes a putative unique 122 amino acid protein, designated U122 in this study. The deduced sequence contains a probable cleaved signal sequence and a C-terminal transmembrane helix, indicating that U122 is likely to be a type I membrane protein. The C-terminal tail also contains a typical ER retrieval motif, KRKTE. U122 was expressed in SARS-CoV infected Vero E6 cells, as it could be detected by Western blot and immunoflourescence analyses. U122 is localized to the perinuclear region of both SARS-CoV infected and transfected cells and co-localized with endoplasmic reticulum (ER) and intermediate compartment markers. Mutational analyses showed that both the signal peptide sequence and ER retrieval motif were functional.