Role of ORF7 in the Genome of SARS-CoV

The aim of this study was to characterize functions of the unknown open-reading frames, Orf7, Orf8 and Orf9 within the Severe acute respiratory syndrome coronavirus (SARS-CoV) genome. We cloned the cDNAs of Orf7, Orf8, Orf9 from the SARS-CoV BJ01 strain were cloned by RT-PCR and constructed into five expression vectors designated as pEGFP-Orf7, pEGFP-Orf8, pEGFP-Orf79, pcDNA3-Orf7 and pcDNA3-Orf8. Hela cells were transfected with the constructs and analyzed for transient expressions by fluorescent analysis. We observed that the expression of pEGFP was enhanced when pcDNA3-Orf7 and pEGFP were co-transfected into Hela cells. Also the expression of pDsRed was increased with pEGFP-Orf7 and pDsRed. More cells which expressed green and red fluorescence at the same time were detected. Based on these results, we demonstrated for the first time that the 63 amino acid protein encoded by Orf7 served as a transcriptional transactivator in SARS-CoV.