A novel coronavirus has been identified as an etiological agent of severe acute respiratory syndrome (SARS). To rapidly identify anti-SARS drugs available for clinical use, we screened a set of compounds that included antiviral drugs already in wide use. Here we report that the HIV-1 protease inhibitor, nelfinavir, strongly inhibited replication of the SARS coronavirus (SARS-CoV). Nelfinavir inhibited the cytopathic effect induced by SARS-CoV infection. Expression of viral antigens was much lower in infected cells treated with nelfinavir than in untreated infected cells. Quantitative RT-PCR analysis showed that nelfinavir could decrease the production of virions from Vero cells. Experiments with various timings of drug addition revealed that nelfinavir exerted its effect not at the entry step, but at the post-entry step of SARS-CoV infection. Our results suggest that nelfinavir should be examined clinically for the treatment of SARS and has potential as a good lead compound for designing anti-SARS drugs.

Murine leukemia virus protease is encoded by the gag-pol gene and is synthesized through suppression of an amber termination codon (retroviral ABSTRACTWe have purified from Moloney murine leukemia virus (Mo-MuLV) a protease that has the capacity of accurately cleaving the polyprotein precursor Pr65m into the mature viral structural proteins. Both the NH2-and COOHterminal amino acid sequences have been determined and aligned with the amino acid sequence deduced from the DNA sequence of Mo-MuLV by other workers. The results show that: (1) the protease is located at the 5' end of thepol gene, and the rst four amino acids are overlapped with the 3' end of the

Although the viral genome is often quite small, it encodes a broad series of proteins. The virus takes advantage of the host-RNAprocessing machinery to provide the alternative splicing capability necessary for the expression of this proteomic diversity. Serinearginine-rich (SR) proteins and the kinases that activate them are central to this alternative splicing machinery. In studies reported here, we use the HIV genome as a model. We show that HIV expression decreases overall SR protein͞activity. However, we also show that HIV expression is significantly increased (20-fold) when one of the SR proteins, SRp75 is phosphorylated by SR protein kinase (SRPK)2. Thus, inhibitors of SRPK2 and perhaps of functionally related kinases, such as SRPK1, could be useful antiviral agents. Here, we develop this hypothesis and show that HIV expression down-regulates SR proteins in Flp-In293 cells, resulting in only low-level HIV expression in these cells. However, increasing SRPK2 function up-regulates HIV expression. In addition, we introduce SR protein phosphorylation inhibitor 340 (SRPIN340), which preferentially inhibits SRPK1 and SRPK2 and down-regulates SRp75. Although an isonicotinamide compound, SPRIN340 (or its derivatives) remain to be optimized for better specificity and lower cytotoxicity, we show here that SRPIN340 suppresses propagation of Sindbis virus in plaque assay and variably suppresses HIV production. Thus, we show that SRPK, a well known kinase in the cellular RNAprocessing machinery, is used by at least some viruses for propagation and hence suggest that SRPIN340 or its derivatives may be useful for curbing viral diseases.HIV ͉ kinase inhibitor ͉ SR protein phosphorylation inhibitor 340 H IV-1 precursor RNA transcribed from proviral DNA integrated in the host cell genome contains all of the transcribed viral reading frames (1). Alternative splicing is essential for producing mRNAs encoding various viral proteins from the limited size of a single precursor mRNA (2). In the early phase of HIV expression, eight splice acceptor sites compete for the splicing machinery to produce the vif, vpu, vpr, nef, env, tat, and rev mRNAs (3). In the late phase of the virus life cycle, singly spliced longer RNA is translated to a polyprotein and then cleaved by HIV protease to generate gag and pol proteins. Several reports show that regulation of the complex splicing pattern can dramatically affect HIV-1 infectivity and pathogenesis (4-6). However, little is known about the molecular mechanism that links this alternative splicing regulation and the dynamics of virus propagation.Alternative splicing depends on the alternative utilization of four 5Ј splice sites and eight 3Ј splice sites (3). The combination of these splice sites are regulated by cis-regulatory elements, which bind cellular heterogeneous nucleoproteins (hnRNPs) of the A, B, and H groups and serine-arginine-rich (SR) proteins (7). SR proteins are highly conserved in eukaryotes and are characterized by having one or two RNA-recognition motifs at the amino termi...

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Retrovirus protease is an enzyme that cleaves gag and gag-pol precursor polyproteins into the functional proteins of mature virus particles. The correct processing of precursor polyproteins is necessary for the infectivity of virus particles: in vitro mutagenesis which introduces deletions into the murine leukaemia virus genome produces a protease-defective virus of immature core form and lacking infectivity. A therapeutic drug effective against disease caused by retrovirus proliferation could likewise interfere with virus maturation. The primary structure has so far been determined for the protease of avian myeloblastosis virus, and of murine, feline and bovine leukaemia viruses. Amino acid sequencing of the retrovirus proteases, either after their purification or from prediction from the nucleotide sequence, shows that they possess the Asp-Thr-Gly sequence characteristic of the aspartyl proteinases. In this report we show that retrovirus proteases belong to the aspartyl proteinase group and demonstrate an inhibition by the aspartyl proteinase-specific inhibitor, pepstatin A, on the activity of bovine leukaemia, Moloney murine leukaemia and human T-cell leukaemia virus proteases.