The tumor suppressor p53 regulates transcription positively and negatively, depending on the target gene. Whereas p53 induces transcription through direct interaction with promoter DNA, the mechanism of p53-mediated transcriptional repression is less well understood. Early reports described the alleviation of p53-mediated repression by inhibitors of apoptosis, suggesting that negative regulation of transcription might occur only in conjunction with programmed cell death. More recently, it has been proposed that certain genes, such as survivin, are repressed by direct association of p53 with their promoters, followed by recruitment of a repressor complex. We show here that p53-mediated negative regulation of transcription could occur independently of apoptosis. In contrast, the amino-terminal transactivation domain of p53 was required for negative regulation of transcription. Similarly, the p53 homologue p73 diminished the expression of survivin and stathmin, depending on its transactivation domain. Mutation of the putative p53 binding site within the survivin promoter did not impair its repression. These observations raised the hypothesis that activation of an effector gene might be required for repression by p53. Strikingly, when the p53-inducible p21/CDKN1A gene was deleted, p53 no longer repressed any one among 11 genes that it downregulates otherwise. Most of these genes were also repressed by ectopic p21 in the absence of p53. Overexpressed c-Myc reduced the transcription of p21/ CDKN1A and impaired p53-mediated repression but did not abolish repression by ectopic p21. Taken together, these results strongly suggest that increased expression of p21/CDKN1A is necessary and sufficient for the negative regulation of gene expression by p53.p53 is a key regulator of cell growth and apoptosis. Its central role in tumor suppression becomes evident by the fact that the p53 gene is mutated in about 50% of human malignancies. p53 acts as a transcription factor, modulating the expression of growth and death regulators. As a result, cell proliferation is suppressed, and/or programmed cell death is induced (1). It is generally accepted that p53 activates a number of promoters through direct interaction with the promoter DNA and the subsequent recruitment of the basal transcription machinery, e.g. the TFIID complex and the p300/CPB histone acetyl transferases. A tetramer of p53 molecules is assembled through the carboxyl-terminal oligomerization domains. This allows the central domains to interact directly with a consensus DNA element. As a consequence, the amino-terminal transactivation domains interact with basal transcription factors,

During infection with adenovirus, massive changes in the transcription of virus genes are observed, suggesting that the expression of cellular genes may also be modulated. To characterize the levels of cellular RNA species in infected cells, cDNA arrays were screened 24 h after infection of HeLa cells with wild-type adenovirus type 5, strain dl309. Despite complete transduction of the cells, fewer than 20 cellular genes (out of 4,600 analyzed and 1,200 found detectable and expressed above background) were altered more than threefold in their corresponding RNA levels compared to mock-infected cells. In particular, the expression of the myc oncogene was reduced at the mRNA level. This reduction was dependent on the replication of virus DNA and partially dependent on the presence of the adenovirus gene products E1B-55 kDa and E4orf6, but not E4orf3. On the other hand, MYC protein had an increased half-life in infected cells, resulting in roughly constant steady-state protein levels. The adenovirus E1A gene product is necessary and sufficient to stabilize MYC. Overexpressed MYC inhibited adenovirus replication and the proper formation of the virus replication centers. We conclude that adenovirus infection leads to the stabilization of MYC, perhaps as a side effect of E1A activities. On the other hand, myc mRNA levels are negatively regulated during adenovirus infection, and this may avoid the detrimental effect of excessive MYC on adenovirus replication.

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A recombinant form of yellow fever virus (YFV) NS3 protease, linked via a nonapeptide to the minimal NS2B co-factor sequence (CF40-gly-NS3pro190), was expressed in Escherichia coli and shown to be catalytically active. It efficiently cleaved the fluorogenic tetrapeptide substrate Bz-norleucine-lysine-arginine-arginine-AMC, which was previously optimized for dengue virus NS2B/3 protease. A series of small peptidic inhibitors based on this substrate sequence readily inhibited its enzymic activity. To understand the structure-activity relationship of the inhibitors, they were docked into a homology model of the YFV NS2B/NS3 protease structure. The results revealed that the P1 and P2 positions are most important for inhibitor binding, whilst the P3 and P4 positions have much less effect. These findings indicate that the characteristics of YFV protease are very similar to those reported for dengue and West Nile virus proteases, and suggest that pan-flavivirus NS3 protease drugs may be developed for flaviviral diseases. INTRODUCTIONYellow fever virus (YFV) is a mosquito-borne flavivirus with a present-day distribution confined largely to equatorial Africa and central South America. The enveloped virus contains a single-and positive-stranded RNA genome that encodes a polyprotein of over 350 kDa (Rice et al., 1985;Chambers et al., 1990a) with the following gene order: 59-C-prM-E-NS1-NS2A-NS2B-NS3-NS4A-NS4B-NS5-39. C, prM and E are structural proteins and NS1-NS5 are nonstructural proteins involved in polyprotein processing and replication. Numerous studies have shown that the YFV NS3 protease, in complex with NS2B, is involved in coand post-translational processing of the viral polyprotein and recognizes cleavage sequences (G/ARRQS/G) with consensus dibasic residues at the P1 and P2 positions to generate the N termini of NS2B, NS3, NS4A and NS5, and additional cleavage sites within core, NS2A and NS4A (Chambers et al., 1991(Chambers et al., , 1993(Chambers et al., , 1995(Chambers et al., , 2005Amberg et al., 1994;Droll et al., 2000).The YFV NS3 protease belongs to the trypsin superfamily and is relatively well conserved amongst members of the family Flaviviridae (Bazan & Fletterick, 1989;Gorbalenya et al., 1989). The essentiality of NS3 protease activity in viral replication, through at least its polyprotein-cleaving activity, has been demonstrated by mutational analysis of the residues predicted to form the canonical serine protease catalytic triad (H53, D77 and S138) (Chambers et al., 1990b(Chambers et al., , 1993(Chambers et al., , 1995(Chambers et al., , 2005Droll et al., 2000).An effective YFV vaccine was developed when the disease caused havoc in North America at the dawn of the 20th century. There still remains a chance that the disease can re-emerge in outbreak proportion because of its increased incidence in the past 25 years and risks of urban YFV in Africa and South America (Barrett & Higgs, 2007). This has led to calls for the development of chemotherapeutic agents for yellow fever so as not to be caught unp...

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