Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.7.48 (transcriptase)
 9,479 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The mechanism of replication of the flavivirus Japanese encephalitis virus (JEV) is not well known. The structures at the 3' end of the viral genome are highly conserved among divergent flaviviruses, suggesting that they may function as cis-acting signals for RNA replication and, as such, might specifically bind to cellular or viral proteins. UV cross-linking experiments were performed to identify the proteins that bind with the JEV plus-strand 3' noncoding region (NCR). Two proteins, p71 and p110, from JEV-infected but not from uninfected cell extracts were shown to bind specifically to the plus-strand 3' NCR. The quantities of these binding proteins increased during the course of JEV infection and correlated with the levels of JEV RNA synthesis in cell extracts. UV cross-linking coupled with Western blot and immunoprecipitation analysis showed that the p110 and p71 proteins were JEV NS5 and NS3, respectively, which are proposed as components of the RNA replicase. The putative stem-loop structure present within the plus-strand 3' NCR was required for the binding of these proteins. Furthermore, both proteins could interact with each other and form a protein-protein complex in vivo. These findings suggest that the 3' NCR of JEV genomic RNA may form a replication complex together with NS3 and NS5; this complex may be involved in JEV minus-strand RNA synthesis.
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PMID:RNA-protein interactions: involvement of NS3, NS5, and 3' noncoding regions of Japanese encephalitis virus genomic RNA. 909 18

The hepatitis C virus is the major causative agent of nonA-nonB hepatitis worldwide. Although this virus cannot be cultivated in cell culture, several of its features have been elucidated in the past few years. The viral genome is a single-stranded, 9.5kb long RNA molecule of positive polarity. The viral genome is translated into a single polyprotein of about 3000 amino acids. The virally encoded polyprotein undergoes proteolytic processing by a combination of cellular and viral proteolytic enzymes in order to yield all the mature viral gene products. The gene order of HCV has been determined to be C-E1-E2-p7-NS2-NS3-NS4A-NS4B-NS5A-NS5B. The mature structural proteins, C, E1 and E2 have been shown to arise from the viral polyprotein via proteolytic processing by host signal peptidases. Conversely, generation of the mature nonstructural proteins relies on the activity of viral proteases. Thus, cleavage at the NS2/NS3 junction is accomplished by a metal-dependent autoprotease encoded within NS2 and the N-terminus of NS3. The remaining cleavages downstream from this site are effected by a serine protease contained within the N-terminal region of NS3. Besides the protease domain, NS3 also contains an RNA helicase domain at its C-terminus. NS3 forms a heterodimeric complex with NS4A. The latter is a membrane protein that has been shown to act as a cofactor of the protease. Whereas the NS5B protein has been shown to be the viral RNA-dependent RNA polymerase, no function has yet been attributed to NS4B and NS5A. The latter is a cytoplasmic phosphoprotein and appears to be involved in mediating the resistance of the hepatitis C virus to the action of interferon.
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PMID:The nonstructural proteins of the hepatitis C virus: structure and functions. 922 25

The polymerase chain reaction was used to amplify a cDNA encoding the catalytic region of ras-guanine nucleotide release factor (ras-GRF1) from mouse embryonic stem cell mRNA. Antibodies directed against this protein were prepared and affinity purified. Western immunoblotting of rat tissue lysates revealed a 140-kDa protein in brain as expected but, in addition, a strongly immunoreactive 54-kDa protein, p54, was identified in pancreas. Expression of ras-GRF1 in pancreas was confirmed at the RNA level by reverse-transcriptase-coupled polymerase chain reaction analysis; p54 may therefore correspond to a form of ras-GRF1 or a closely related protein. The cellular and subcellular localization of p54 was investigated by enzyme-linked immunocytochemistry and immunogold electron microscopy. In the pancreas, p54 was expressed primarily in acinar cells, where it was localized along the basolateral and apicolateral plasma membranes. Indirect immunofluorescence microscopy of cultured acini further indicated that the plasma membrane localization of p54 was dependent on the maintenance of the acinar histotype and organized acinar structure. When primary acinar cells were permitted to dissipate into monolayer cultures devoid of zymogen granules, ras-GRF1 staining became cytosolic. Our results suggest that ras-GRF1 is involved in the structure and function of the pancreas.
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PMID:A 54-kDa protein related to ras-guanine nucleotide release factor expressed in the rat exocrine pancreas. 923 29

At present, the mechanism of replication of the HCV genome remains unclear. Recently, NS5B and NS3 of HCV have been shown to exhibit RNA-dependent RNA polymerase and helicase activities, respectively, both of which are indispensable for virus RNA replication. In this study, we examined the complex formation of NS5B with NS3 and NS4A, a cofactor for NS3. We show here that NS5B forms a complex with NS3 through an amino-terminal portion of NS3. The NS3-NS5B complex formation took place both in the presence and absence of NS4A. We also demonstrate that NS5B form a complex with NS4A in the absence of NS3. These results suggest that NS3, NS4A and NS5B interact with each other to form a complex that functions as part of the replication machinery of HCV.
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PMID:Complex formation of NS5B with NS3 and NS4A proteins of hepatitis C virus. 951 71

The hepatitis C virus (HCV) was identified as the major causative agent of posttransfusion and community-acquired non-A, non-B hepatitis throughout the world. It is an enveloped virus with a plus-strand RNA genome encoding a polyprotein of about 3,010 amino acids. This polyprotein is cleaved co- and posttranslationally into mature viral proteins by host cell signal peptidases and 2 viral enzymes designated the NS2-3 proteinase and the NS3/4A proteinase complex. It is assumed that virus replication takes place in a membrane-associated complex containing at least 2 viral enzymatic activities: the NS3 nucleoside triphosphatase (NTPase)/helicase and the NS5B RNA-dependent RNA polymerase (RdRp). Based on their important role for the viral life cycle and the wealth of information available for related cellular and viral proteins, the NS3/4A serine-type proteinase complex, the NS3 NTPase/helicase and the NS5B RdRp are the most attractive targets for development of HCV-specific antiviral therapies. This review will summarize our current knowledge about structure and function of these proteins and describe approaches pursued to identify effective antiviral compounds.
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PMID:Candidate targets for hepatitis C virus-specific antiviral therapy. 967 42

Hepatitis C virus (HCV) infection is a major health problem that leads to cirrhosis and hepatocellular carcinoma in a substantial number of infected individuals, estimated to be 100-200 million worldwide. Unfortunately, immunotherapy or other effective treatments for HCV infection are not yet available, and interferon administration has limited efficacy. Different approaches to HCV therapy are being explored, and these include inhibition of the viral proteinase, helicase, and RNA-dependent RNA polymerase and development of a vaccine. Here we present the design of selective inhibitors with nanomolar potencies of HCV NS3 proteinase based on eglin c. These eglin c mutants were generated by reshaping the inhibitor active site-binding loop, and the results emphasize the role played by residues P5-P4' in enzyme recognition. In addition, alanine scanning experiments provide evidence that the N terminus of eglin c also contributes to NS3 binding. These eglin inhibitors offer a unique tool for accurately assessing the requirements for effective inhibition of the enzymatic activity of NS3 and at the same time can be considered lead compounds for the identification of other NS3 inhibitors in targeted design efforts.
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PMID:Design of selective eglin inhibitors of HCV NS3 proteinase. 970 81

Four bovine viral diarrhea virus type 2 (BVDV-2) pairs consisting of cytopathogenic (cp) and noncp BVDV-2 were isolated during an outbreak of mucosal disease. Comparative sequence analysis showed that the four noncp BVDV-2 isolates were almost identical. For the cp BVDV-2 isolates, viral subgenomic RNAs were shown by Northern blot to have a length of about 8 kb, which is about 4.3 kb shorter than the genome of noncp BVDV. Cytopathogenicity and the expression of NS3 were both strictly correlated to the presence of viral subgenomic RNAs. By reverse transcription-PCR, Southern blot analysis, and nucleotide sequencing, a set of 11 unique subgenomes was identified with up to 5 different subgenomes isolated from one animal. To our knowledge, this is the first report on isolation of a set of pestiviral subgenomes from individual animals. Common features of the BVDV-2 subgenomic RNAs include (i) deletion of most of the genomic region encoding the structural proteins, as well as the nonstructural proteins p7 and NS2, and (ii) insertion of cellular (poly)ubiquitin coding sequences. Three subgenomes also comprised 15 to 75 nucleotides derived from the 5' part of the NS2 gene. Comparisons of the obtained nucleotide sequences revealed that the different BVDV-2 subgenomes evolved from the respective noncp BVDV-2 by RNA recombination. The presence of short regions of sequence similarity at several crossing-over sites suggests that base pairing between the nascent RNA strand and the acceptor RNA template facilitates template switching of the BVDV RNA-dependent RNA polymerase.
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PMID:Nonhomologous RNA recombination in bovine viral diarrhea virus: molecular characterization of a variety of subgenomic RNAs isolated during an outbreak of fatal mucosal disease. 1036 14

Hepatitis C virus (HCV) has a positive-stranded RNA genome of about 9.5 kb and a large open reading frame encoding a precursor polyprotein of ca. 3,000 amino acids (aa). This polyprotein is cleaved by host cellular signalase(s) and viral proteases into 10 viral proteins in the order of NH(2)-Core-E1-E2-p7-NS2-NS3-NS4A-NS4B-NS5A-NS 5B-COOH. Core and E1/E2 are considered to be a capsid protein and envelope glycoproteins, respectively. NS2-NS5B are putative nonstructural proteins involved in the replication of HCV. NS2/3 is a metalloprotease which cleaves in cis at the NS2/3 junction. NS3 possesses serine protease and RNA helicase activities and is responsible for the cleavage of the remaining nonstructural proteins. NS4A is suggested to be a cofactor for NS3 protease. Although the function of p7, NS4B and NS5A are still unknown, an association of a mutation in NS5A with a susceptibility to interferon (IFN) has been reported. NS5B possesses an RNA-dependent RNA polymerase activity. Most of the current findings in HCV proteins depend on expression studies of HCV cDNA clones because of the lack of an efficient replication system in cell cultures. Therefore, a final assignment of cleavages and functions of HCV proteins has to await the propagation of HCV in cell cultures.
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PMID:Processing and functions of Hepatitis C virus proteins. 1051 68

Hepatitis C virus (HCV) infection is a leading cause of chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma worldwide. Therapeutic options for hepatitis C are limited. Standard monotherapy with interferon-alpha leads to a sustained response in only 10-20% of patients. Recent studies have shown improved sustained response rates for the combination of interferon-alpha and ribavirin. Despite these improvements, more effective therapies are needed. A variety of alternative agents are currently being evaluated in clinical trials. Recent advances in the molecular virology of hepatitis C have identified specific antiviral targets such as the viral NS3 serine protease, the RNA helicase, and the RNA-dependent RNA polymerase. In addition, gene therapeutic strategies aimed at inhibiting HCV gene expression and replication as well as immunotherapeutic concepts aimed at enhancing the cellular immune response against HCV are being explored in various experimental systems. These and other novel antiviral strategies may complement the existing therapeutic modalities in the future.
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PMID:Current and evolving therapies for hepatitis C. 1056 26

Infection with the hepatitis C virus (HCV) is the major cause of nonA-nonB hepatitis worldwide. Although this virus cannot be cultivated in vitro, several of its key features have been elucidated in the past few years. The viral genome is a positive-sense, single-stranded, 9.6 kb long RNA molecule. The viral genome is translated into a single polyprotein of about 3000 amino acids. The viral polyprotein is proteolytically processed by the combination of cellular and viral proteinases in order to yield all the mature viral gene products. The genomic order of HCV has been shown to be C-E1-E2-p7-NS2-NS3-NS4A-NS4B-NS5A-NS5B. C, E1 and E2 are the virion.structural proteins. The function of p7 is currently unknown. These proteins have been shown to arise from the viral polyprotein via proteolytic processing by the host signal peptidases. Generation of the mature nonstructural proteins, NS2 to NS5B, relies on the activity of viral proteinases. Cleavage at the NS2/NS3 junction is accomplished by a metal-dependent autocatalytic proteinase encoded within NS2 and the N-terminus of NS3. The remaining cleavages downstream from this site are effected by a serine proteinase also contained within the N-terminal region of NS3. NS3 also contains an RNA helicase domain at its C-terminus. NS3 forms a heterodimeric complex with NS4A. The latter is a membrane protein that has been shown to act as a cofactor of the proteinase. While no function has yet been attributed to NS4B, it has recently been suggested that NS5A is involved in mediating the resistance of the hepatitis C virus to the action of interferon. Finally, the NS5B protein has been shown to be the viral RNA-dependent RNA polymerase.
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PMID:Molecular virology of the hepatitis C virus. 1062 60


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