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A novel coronavirus is the causative agent of the current epidemic of severe acute respiratory syndrome (SARS). Coronaviruses are exceptionally large RNA viruses and employ complex regulatory mechanisms to express their genomes. Here, we determined the sequence of SARS coronavirus (SARS-CoV), isolate Frankfurt 1, and characterized key RNA elements and protein functions involved in viral genome expression. Important regulatory mechanisms, such as the (discontinuous) synthesis of eight subgenomic mRNAs, ribosomal frameshifting and posttranslational proteolytic processing, were addressed. Activities of three SARS coronavirus enzymes, the helicase and two cysteine proteinases, which are known to be critically involved in replication, transcription and/or post-translational polyprotein processing, were characterized. The availability of recombinant forms of key replicative enzymes of SARS coronavirus should pave the way for high-throughput screening approaches to identify candidate inhibitors in compound libraries. INTRODUCTIONSevere acute respiratory syndrome (SARS) is a lifethreatening form of pneumonia (Peiris et al., 2003a). In the course of a few months in 2003, an epidemic emerged that has spread from its likely origin in Guangdong Province, China, to 32 countries. By 11 June 2003 more than 8400 cases and 789 deaths had been recorded by the World Health Organization. The rapid transmission by aerosols (and probably also the faecal-oral route) and the high mortality rate make SARS a global threat for which no efficacious therapy is available. There is now clear evidence that SARS is caused by a previously unknown coronavirus, provisionally termed SARS coronavirus (SARS-CoV) (Peiris et al., 2003b;Drosten et al., 2003;Ksiazek et al., 2003;Fouchier et al., 2003). Genome sequences of SARS-CoV isolates obtained from a number of index patients have been published recently and provide important information on the organization, phylogeny and variability of the 29?7 kb positive-strand RNA genome of SARS-CoV (Rota et al., 2003;Marra et al., 2003;Ruan et al., 2003). By analogy with other coronaviruses (Lai & Holmes, 2001;Gorbalenya, 2001), SARS-CoV gene expression is expected to involve complex transcriptional, translational and post-translational regulatory mechanisms, whose molecular details remain to be determined. SARS-CoV genome expression starts with the translation of two large replicative polyproteins, pp1a (486 kDa) and pp1ab (790 kDa), which are encoded by the viral replicase gene (21 221 nt) that comprises ORFs 1a and 1b (Fig. 1). Expression of the ORF1b-encoded region of pp1ab is predicted to involve ribosomal frameshifting into the 21 frame just upstream of the ORF1a translation termination codon (Brierley et al., 1989). The pp1a and pp1ab polyproteins are processed by viral proteinases to yield the functional components of the membrane-bound replicase complex (Ziebuhr et al., 2000). In contrast to most other coronaviruses, which use three proteinase activities for replicase polyprotein processing (Ziebuhr et ...

The outbreak of SARS warrants the search for antiviral compounds to treat the disease. At present, no specific treatment has been identified for SARS-associated coronavirus infection. We assessed the antiviral potential of ribavirin, 6-azauridine, pyrazofurin, mycophenolic acid, and glycyrrhizin against two clinical isolates of coronavirus (FFM-1 and FFM-2) from patients with SARS admitted to the clinical centre of Frankfurt University, Germany. Of all the compounds, glycyrrhizin was the most active in inhibiting replication of the SARS-associated virus. Our findings suggest that glycyrrhizin should be assessed for treatment of SARS.

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