Characterization of a unique group-specific protein (U122) of the severe acute respiratory syndrome coronavirus
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Date
2004Author
Fielding, Burtram C.
Tan, Yee-Joo
Shen, Shuo
Tan, Timothy H.P.
Ooi, Eng-Eong
Lim, Seng Gee
Hong, Wanjin
Goh, Phuay-Yee
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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 CoV 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 CoVs, 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 endoplasmic reticulum (ER) retrieval motif, KRKTE. U122 was expressed in SARS-CoVinfected
Vero E6 cells, as it could be detected by Western blot and immunofluorescence analyses. U122 is
localized to the perinuclear region of both SARS-CoV-infected and transfected cells and colocalized with ER
and intermediate compartment markers. Mutational analyses showed that both the signal peptide sequence
and ER retrieval motif were functional.