Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

Human cells derived from both normal and neoplastic tissues can be infected by Mason-Pfizer monkey virus (MPMV) without accompanying cytopathology. Infection of cell cultures such as human rhabdomyosarcoma (A204) results in a persistenly infected cell line which can be subcultured over 30 sequential culture passages without significant change in phenotype properties according to reverse, transcriptase (RT), MPMV p27 antigen content, virus particle count and infectivity titre. Productive virus infections were established at relatively low virus particle (VP) input multiplicities (p.i.m.; about 0.06 VP/cell) In A204 cell cultures. At higher p.i.m. (about 600 to 6000 VP/cell) newly synthesized virus was detected within 4 days post infection. Although virus production was cumulative following primary infection, after subculture of infected cultures MPVM production was greater during active cell division. Using synchronization techniques, MPMV replication in persistently infected cultures was found to be cell cycle-dependent. The major internal antigen, p27, was synthesized in G2 and newly synthesized virus particles were released predominantly during mitosis and early G1. Colcemid arrest of cells during mitosis inhibited subsequent MPMV release. Consequently, production of extracellular virus depends upon the progression of cells through the mitotic stage. These data, which provided a basic understanding of the virus-host relationship that occurs in primate cells productively infected with MPMV, were used as a guideline for isolating MPMV-like viruses from experimentally and naturally infected Rhesus monkey.
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PMID:Characterization of infection and replication of Mason-Pfizer monkey virus in human cell cultures. 11 35

Adeno-associated virus (AAV) is a nonpathogenic parvovirus which normally requires helper adenovirus or herpes-virus for replication. We examined the growth of AAV type 2 in human lymphocytes and its possible interaction with HIV-1. Three B cell lines (CK-B, HS-2, and UC729) and four T cell lines (Molt-4, Jurkat, HUT78, and HUT78+HIV, which is persistently infected with HIV-1) were infected with AAV either in the presence or in the absence of adenovirus. AAV DNA was found in cells of all the lines following incubation with the virus, indicating absorption. AAV DNA replication occurred in most cell lines without particular preference for B or T cells, but only in the presence of helper virus, either adenovirus or Epstein-Barr virus. Expression of AAV proteins was examined by immunoblotting and ELISA, using sera specific for AAV Rep or capsid proteins. The level of AAV protein synthesis correlated with the efficiency of AAV DNA replication, and both varied between cell lines. The yield of infectious AAV was low in most cases, except in one T4 line (Jurkat), where AAV replication and protein synthesis in the presence of adenovirus were very extensive. In HUT78+HIV cells both adenovirus and AAV (in the presence of Ad2) replicated efficiently. The effects of adenovirus plus AAV coinfections on HIV-1 replication, measured by reverse-transcriptase (RT) activity, were mild. Infection with adenovirus or AAV alone resulted in a 60-70% increase in RT activity, while infection with AAV plus adenovirus resulted in a 20% decrease in RT activity. The yield of infectious AAV in this cell line was very low.
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PMID:Replication of adeno-associated virus type 2 in human lymphocytic cells and interaction with HIV-1. 137 38

Infection by ribonucleic acid (RNA) bacteriophage R23 inhibited the synthesis of beta-galactosidase in Escherichia coli. The inhibition, although not complete, was apparent shortly after infection and was maximal after the first 20 min of infection. R23 diminished the beta-galactosidase-synthesizing capacity when inducer was added after phage infection, but not when infection followed inducer removal. These findings suggested that the primary effect of R23 on enzyme-forming capacity was limitation of synthesis of enzyme-specific messenger RNA. Studies with ultraviolet irradiated phage and amber mutants of R23 indicated that the inhibitory process could be separated into two phases. Early inhibition did not require the expression of the viral genome, whereas late inhibition required the expression of the viral RNA synthetase cistron.
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PMID:Effect of infection with ribonucleic acid bacteriophage R23 on the inducible synthesis of beta-galactosidase in Escherichia coli. 491 Aug 18

Infection of plants or protoplasts with turnip crinkle virus (TCV), a monopartite RNA virus, results in the synthesis of the genomic RNA and two subgenomic (sg) RNAs. The transcription start site for the 1.45-kb sgRNA was previously mapped to position 2606 (J. C. Carrington, T. J. Morris, P. G. Stockley, and S. C. Harrison, (1987). J. Mol. Biol. 194, 265-276) corresponding to position 2607 in the TCVms isolate and the start site for the 1.7-kb sgRNA has now been mapped to position 2333 in TCVms. A 96-base sequence (90 bases upstream and 6 bases downstream) encompassing the transcription start site for the 1.45-kb sgRNA was sufficient for full promoter activity. Similarly, a 94-base sequence (90 bases upstream and 4 bases downstream) encompassing the start site was required for full activity of the 1.7-kb sgRNA promoter. The 1.45-kb sgRNA promoter, but not the 1.7-kb sgRNA promoter, was able to direct synthesis of a nontemplate RNA in vitro using partially purified TCV RNA-dependent RNA polymerase. Computer generated secondary structures for the two sgRNA promoters revealed an extensive hairpin just upstream from the transcription start site. Comparisons of corresponding sequences from related viruses indicates higher sequence conservation for the 1.45-kb sgRNA promoter compared with the 1.7-kb sgRNA promoter, despite the latter's location within the RNA-dependent RNA polymerase open reading frame.
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PMID:Analysis of the two subgenomic RNA promoters for turnip crinkle virus in vivo and in vitro. 918 1

Mammalian reovirus virions undergo partial disassembly of the outer capsid upon exposure to proteases in vitro, producing infectious subvirion particles (ISVPs) that lack protein sigma3 and contain protein mu1/mu1C as endoprotease-generated fragments mu1delta/delta and phi. ISVPs are thought to be required for two early steps in reovirus infection: membrane penetration and activation of the particle-bound viral transcriptase complexes. Genetic and biochemical evidence implicates outer-capsid protein mu1 in both these steps. To determine whether the cleavage of mu1/mu1C is relevant to the unique properties of ISVPs, we analyzed the properties of novel subvirion particles that lacked sigma3 yet retained mu1/mu1C in an uncleaved but cleavable form. These detergent-plus-protease subvirion particles (dpSVPs) were produced by treating virions with chymotrypsin in the presence of micelle-forming concentrations of alkyl sulfate detergents. Infections with dpSVPs in murine L or canine MDCK cells provided evidence that the cleavage of mu1/mu1C during viral entry into these cells is dispensable for reovirus infection. Additionally, dpSVPs behaved like ISVPs in their capacity to permeabilize lipid bilayers and to undergo transcriptase activation in vitro, supporting the conclusion that cleavage of mu1/mu1C to mu1delta/delta and phi during viral entry is not required for either membrane penetration or transcriptase activation in cells. The capacity of alkyl sulfate detergents to inhibit the cleavage of mu1/mu1C in a reversible fashion suggests a specific association between virus particle and detergent micelles that may mimic virus particle-phospholipid membrane interactions during reovirus entry into cells.
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PMID:Protease cleavage of reovirus capsid protein mu1/mu1C is blocked by alkyl sulfate detergents, yielding a new type of infectious subvirion particle. 942 Feb 47

A recently discovered non-A-E hepatitis virus has been designated as hepatitis G virus (HGV) and identified as a new member of the Flaviviridae family. Infection by this virus is thought to be associated with blood-borne hepatitis and usually in the presence of hepatitis C or hepatitis B virus (HBV) infection. In this study, the presence of HGV-RNA in serum or plasma and the prevalence of antibodies against an HGV envelope protein (E2) were investigated in patients undergoing chronic hemodialysis using a sensitive reverse-transcriptase polymerase chain reaction and an enzyme-linked immunosorbent assay, respectively. HGV-RNA was detected in 19 of 112 patients investigated (17%) and anti-E2 antibodies were detected in 15 of 106 patients studied (14.2%). With the exception of two patients, the appearance of anti-E2 is associated with the clearance of serum HGV-RNA. The total prevalence of current (HGV-RNA positivity) and/or past (anti-E2 positivity) HGV infection in this patient population is thus 28.6% (32 of 112 patients were positive for serum HGV-RNA and/or anti-E2 antibodies). In apparently healthy blood donors, serum HGV-RNA was detected in four of 358 individuals (1.12%) and anti-E2 was not detected in 50 individuals investigated. From the 19 patients with serum HGV-RNA positivity, nine were coinfected with other hepatitis viruses (seven with HBV; one with HBV, hepatitis C virus [HCV], and hepatitis D virus; and one with HBV and cytomegalovirus). Thirteen of 15 patients with anti-E2 positivity (10 were positive for only anti-E2 and three were also positive for anti-HBc) had no detectable HGV-RNA. In two patients, both HGV-RNA and anti-E2 antibodies were concomitantly present (both patients were coinfected with HCV or HBV). Of the HGV-infected patients, only three who were coinfected with HBV showed elevated serum alanine aminotransferase levels. The serum HCV-RNA and/or anti-HCV were detected in five (4.5%) of 112 patients. From these findings, we conclude that there is a high prevalence of HGV infection (28.6%) compared with HCV (4.5%) in patients undergoing hemodialysis in our hospital. However, approximately 50% of patients had spontaneously lost the viremia and developed anti-HGV-E2 antibodies. We confirm that HGV infection alone is not associated with elevated serum transaminases, and the appearance of anti-HGV-E2 is usually accompanied with clearance of serum HGV-RNA. In contrast to the results of our previous study, the majority of patients infected with HGV are not coinfected with HCV, indicating that HGV is capable of independent transmission. It is likely that there is a preferential HGV acquisition in the hemodialysis unit. The clinical significance of long-term infection with HGV remains to be established.
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PMID:High prevalence of hepatitis G virus infection compared with hepatitis C virus infection in patients undergoing chronic hemodialysis. 946 14

Enteric infection of mice with reovirus serotype 1 elicits antibody and cytotoxic T-lymphocytes in gut-associated lymphoid tissue (GALT). This led to the hypothesis that T-helper 1 (Th1) and T-helper 2 (Th2) responses develop in GALT. Reverse transcriptase-polymerase chain reactions on RNA from Peyer's patches (PP), intraepithelial lymphocytes (IEL), and lamina propria (LP) lymphocytes demonstrated that interferon (IFN)-gamma message was increased in PP and IEL, but not in LP following infection. No increase in mRNA for interleukin (IL)-4, IL-5, or IL-6 was detected. IFN-gamma, IL-5, and IL-6 were produced in in vitro cultures of PP 4-10 days postinfection. PP and spleen lymphocytes from infected mice produced IFN-gamma, but no IL-5 following in vitro restimulation. Infection also induced production of mRNA for the beta2 chain of the IL-12 receptor in PP. We conclude that reovirus induces robust Th1 and weak Th2 cell responses in GALT.
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PMID:T-Helper 1 and T-helper 2 cytokine responses in gut-associated lymphoid tissue following enteric reovirus infection. 974 58

Infection of plants or protoplasts with turnip crinkle virus (TCV) results in the synthesis of the genomic RNA and two subgenomic (sg) RNAs of 1.7 kb and 1.45 kb, respectively. Both of the sgRNA promoters were characterized previously and their secondary structures predicted by computer analysis [J. Wang and A. E. Simon (1997). Virology 232, 174-186]. Secondary structure-sensitive chemical and enzymatic probes have now been used to determine the structure of the promoter directing synthesis of the 1.45-kb sgRNA, namely the 1.45-kb sgRNA promoter, in solution. The newly obtained structure conforms with the previously predicted hairpin structure except for the hairpin base: four CG base pairs and a CA bulge are present instead of an A bulge. Studies of deletions within the 96-nucleotide (nt) 1.45-kb sgRNA promoter defined a minimal 30-nt core sequence as essential for promoter activity: a 21-nt hairpin and a 9-nt flanking single-stranded sequence. Mutational analysis in the stem section of the core promoter supported a role for the primary sequence and secondary structure in promoter activity. Sequence alterations in the flanking single-stranded region further suggest that the sequence CCCAUUA, encompassing the transcription start site, is required for efficient transcription of the 1.45-kb sgRNA by the TCV RNA-dependent RNA polymerase in vivo.
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PMID:Minimal sequence and structural requirements of a subgenomic RNA promoter for turnip crinkle virus. 991 91

The recent discovery of chemokine receptors as coreceptors for human immunodeficiency virus-type 1 (HIV-1) entry offers new avenues for investigating the pathogenesis of acquired immunodeficiency syndrome (AIDS)-related cytopenias. To this end, we sought to (1) phenotype human hematopoietic cells for CD4 and the HIV-1 coreceptors CXCR4, CCR5, CCR3, and CCR2b; (2) correlate CD4 and chemokine receptor expression with their susceptibility to HIV-1 infection; and (3) examine any potential interplay between inflammatory cytokines released during HIV-1 infection and regulation of chemokine receptor expression. Fluorescence-activated cell sorting (FACS) analysis of bone marrow mononuclear cells (BMMNC), cells derived from serum-free expanded hematopoietic lineages (colony-forming unit-granulocyte-macrophage [CFU-GM], colony-forming unit-megakaryocyte [CFU-Meg], and burst-forming unit-erythroid [BFU-E]), and CD34(+) cells showed differential expression of chemokine receptors and CD4 with some lineage specificity. Significantly, FACS-sorted CXCR4(+)/CD34(+) cells had the same clonogeneic potential as CXCR4(-)/CD34(+) cells. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of FACS-sorted human candidate stem cells (HSC; CD34(+), c-kit+, Rho123(low)) showed the presence of CXCR4 mRNA but not CD4 mRNA. Infection studies with HIV-1 Env-pseudotyped luciferase reporter viruses indicated that X4 Env (CXCR4-using) pseudotypes infected megakaryocytic cells, whereas R5 Env (CCR5-using) pseudotypes did not. Similarly, R5 but not X4 Env-pseudotyped viruses infected granulocyte-macrophage cells in a CD4/CCR5-dependent manner. Erythroid cells were resistant to R5 or X4 viral infection. Finally, we found that gamma-interferon treatment upregulated CXCR4 expression on primary hematopoietic cells. In summary, the delineation of chemokine receptor expression on primary hematopoietic cells is a first step towards dissecting the chemokine-chemokine receptor axes that may play a role in hematopoietic cell proliferation and homing. Furthermore, susceptibility of hematopoietic cells to HIV-1 infection is likely to be more complicated than the mere physical presence of CD4 and the cognate chemokine receptor. Lastly, our results suggest a potential interplay between gamma-interferon secretion and CXCR4 expression.
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PMID:Coreceptor/chemokine receptor expression on human hematopoietic cells: biological implications for human immunodeficiency virus-type 1 infection. 994 56

Reverse transcriptase (RT) isolated from Rous sarcoma virus (RSV) consists of heterodimeric RTalphabeta, RTalpha, and RTbeta. The alpha subunit (63 kDa) contains an N-terminal polymerase and a C-terminal RNase H domain. The N terminus of beta (95 kDa) corresponds to alpha with the integrase domain attached to the C terminus (32 kDa). We have constructed baculoviruses expressing the genes for alpha or beta or the entire pol (99 kDa). Infection of insect cells with recombinant virus yielded highly active and soluble RSV RT enzymes that could be purified to >90% homogeneity. HPLC gel filtration showed that alpha is a dimeric enzyme that can be partially monomerized upon the addition of 45% Me(2)SO. DNA synthesis on DNA-DNA and DNA-RNA primer-templates in the presence of competitor substrates revealed that alphabeta and beta as well as alpha are processive polymerases. However, the affinity of beta and alphabeta for primer-template substrates appears to be higher than that of alpha. All RSV enzymes investigated have the potential to displace RNA-RNA duplexes more efficiently than human immunodeficiency virus type 1 RT. Unlike human immunodeficiency virus type 1 RT, RSV RTs can catalyze an initial RNase H endonucleolytic cleavage of the RNA template but not a 3' --> 5' directed processing activity.
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PMID:Soluble Rous sarcoma virus reverse transcriptases alpha, alphabeta, and beta purified from insect cells are processive DNA polymerases that lack an RNase H 3' --> 5' directed processing activity. 1047 89


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