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)

The alpha, beta2, and alphabeta forms of the RNA-dependent DNA polymerase of avian sarcoma virus B77 grown in duck embryo fibroblasts have been compared with respect to several kinetic properties. The following results were obtained. 1. The Km values for dTTP and dGTP for enzyme forms alpha, beta2, and alphabeta were 77, 39, and 74, and 6.8, 3.1, and 6.1 micronM, respectively. 2. The affinity of 70 S Rous sarcoma virus RNA for enzyme form alphabeta was about twice that for the other two forms. 3. The relative specific activities of the three enzyme forms on synthetic primer-templates such as poly(rA)-poly(dT) were almost the same. The viral 70 S RNA-dependent specific activities were 2 to 3 orders of magnitude lower and in the ratio of 1:3:5 for enzyme forms alpha:beta2:alphabeta. Addition of exogenous oligo(dT) stimulated the 70 S viral RNA-dependent activity of enzyme forms alphabeta and beta2 by a factor of 3, and that of enzyme form alpha by a factor of 30, so that it then became the most active transcriptase of viral 70 S RNA. 4. The largest transcripts formed by the three enzyme forms with 70 S viral RNA as primer-template were about 4,500 nucleotides long. About one-third of the total amount of polynucleotides polymerized by the alphabeta enzyme was in the form of such transcripts. This proportion was far higher than for the other two enzyme forms. 5. All three enzyme forms were capable of transcribing single-stranded into double-stranded DNA. 6. The 3-propylcyclohexyl piperidyl derivative of rifamycin SV, at a concentration of 100 microng/ml, inhibited enzyme forms beta2 and alphabeta by over 99.5 and 96%, respectively, but enzyme form alpha by only about 60%. 7. The beta2 and alphabeta forms of the enzyme were processive DNA polymerases, the alpha form a nonprocessive polymerase. 8. In general, these results indicate that in most respects the properties of the dimeric enzyme forms resemble each other much more closely than those of the alpha form. In some very important respects, such as affinity for viral RNA and the size of transcripts formed from it, the alphabeta enzyme form performs significantly better than either of the other two enzyme forms.
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PMID:RNA-dependent DNA polymerase of avian sarcoma virus B77. II. Comparison of the catalytic properties of the alpha, beta2, and alphabeta enzyme forms. 6 35

Reverse transcriptase activity was detected in the supernatants of rat embryo fibroblast cell cultures transformed by HSV types 1 and 2 at either the sub-optimal temperature of 20 degrees C or the supra-optimal temperature of 42 degrees C. Rat cells clones which had been transformed at 20 degrees C contained higher levels of C-type virus DNA polymerase than did cell clones which had been transformed at 42 degrees C. Syncytia formation typical for C-type RNA viruses occurred at passages higher than 24. The activation of endogenous C-type RNA viruses was independent of the virus and transformation method used.
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PMID:Activation of an endogenous C-type RNA virus in rat embryo cells after transformation by herpes simplex virus types 1 and 2. 7 May 8

An oncornavirus immunologically similar to oncornaviruses type D previously isolated from human continuous cells was detected in continuous cells of mammary cancer (SH3). The culture produces structures having densities of 1.18--1.19 and 1.22 g/ml which contain high molecular RNA (68S) and reverse-transcriptase activity. The similarity of this virus with other oncornaviruses was also demonstrated in molecular hybridization experiments.
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PMID:[Detection of oncornavirus type D in continuous breast cancer cells]. 7 58

Continuous monitoring of enzymes, particularly those involved in nucleic acid synthesis could be a useful means of detecting infections and abnormalities in cells in culture. Model systems using mouse (3T3), human (MRC-5) and chick embryo cells infected with RNA tumour viruses were studied. Reverse transcriptase activities were determined by the incorporation of (3H) nucleotides into synthetic primer-templates or into complementary DNA of endogenous RNA and characterised by their specificity for primer-templates dT12-18.rAn, dG12-18.rCn, dT12-18.DAn and dG10.rCmn, their requirements for metal ions and inhibition by antisera. Measurement of reverse transcriptase is a more sensitive method than the COFAL test for the detection of RAV infection of chick cells. Iododeoxyuridine, bromodeoxyuridine and dexamethasone, which can induce latent C viruses, have no effect on MRC-5 cells; no increases in reverse transcriptase were detected and no C particles were seen by electron microscopy. Solid tumours developed in immunosuppressed mice injected s/c with 3T3 and MRC-5 cells chronically infected with MLV but none formed after injection of cells or virus suspension alone. Thymidine kinase activities of WI-38 and MRC-5 cells are greatly increased by infection with CMV or transformation with SV40. Mammalian tumours and tumour cell lines also show a high specific activity of cytoplasmic thymidine kinase.
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PMID:Reverse transcriptase and thymidine kinase as markers for tumorigenicity and viral contamination of cells. 7 84

Two maxima of optic density were observed at zones of gravity 1.27 g/ml and 1.15-1.16 g/ml by sedimentation equilibrium in sucrose gradient of cultural fluid, obtained from the transplantable cells of the HEP-2 strain and concentrated by ultracentrifugation. These fractions thus isolated were tested for presence of RNA- and DNA-dependent DNA-polymerase. The structures with the density of 1.15-1.16 g/ml were identified with the oncornaviruses on the basis of characteristics flotating density, presence of RNA-dependent DNA-polymerase. Analyses of products of RNA- and DNA-dependent polymerases reaction, flotating density of oncornaviral nucleotides in sucrose and CsCl gradients are presented. The optimal conditions for reverse-transcriptase reaction of virions of D type viruses are characterized.
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PMID:[Further study of spontaneous virus production using transplantable HEp-2 cells as a model]. 7 26

Reverse transcriptase from foamy virus, strain H4188 was estimated and purified. The enzyme has the following characteristics: 1. The reaction utilized preferentially oligo (dT) poly (rA) as a primer-template; however, the synthetic primer-template oligo (dT) poly (dA) could also be used to some extent. 2. The reaction utilized oligo (dG) poly (rC) as a primer-template with very low efficiency. 3. The crude virus preparation had a detectable endogenous reaction using the four deoxyribonucleotides for DNA polymerization. 4. The cation requirement for the enzyme reaction was much more biased for Mn++ than for Mg++ ions. 5. The molecular weight of the partially-purified enzyme was estimated to be about 80,000. Aggregates of 240,000 daltons were also seen. The activity of this enzyme was not inhibited by antisera against the reverse transcriptases of various type C RNA viruses, namely, feline endogenous leukemia virus, RD 114, Woolly simian sarcoma virus (SSV-1) and avian myeloblastosis virus (AMV). Antiserum against Rauscher leukemia virus (RLV) enzyme was marginally active against foamy virus enzyme, perhaps indicating a slight cross-reaction. The biochemical characteristics of foamy virus reverse transcriptase seemed to be very close to those of the type C RNA viruses, but the immunological reaction proved that the foamy virus reverse transcriptase was distinct from the others.
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PMID:Reverse transcriptase of foamy virus. Purification of the enzymes and immunological identification. 7 44

Reverse transcriptase (RT; RNA-dependent DNA nucleotidyltransferase) from Rauscher leukemia virus is synthesized in infected cells by way of a read-through poly- rotein of 200,000 molecular weight. This polyprotein (Pr200(gag-pol)) was precipitated by antiserum to RT; in a previous study all the monospecific antisera to gag proteins recognized Pr200(gag-pol). Pr200(gag-pol) contains both p30 and RT peptide sequences. Intermediate RT-related precursors of 145,000 (Pr145(pol)), 135,000 (Pr135(pol)), and 125,000 (Pr125(pol)) molecular weights were specifically recognized by precipitation from infected cell extracts by antiserum to RT. These proteins shared methionine-containing tryptic peptide sequences with a virion polypeptide of 80,000 molecular weight (p80(pol)) precipitate by antiserum to RT. Purification of active RT enzyme from virions labeled with [(3)H]methionine showed that p80(pol) was the major component, based on analysis by gel electrophoresis and tryptic peptide mapping experiments. A polypeptide (Pr80(pol)), similar in size to mature viral p80(pol), was also precipitated from infected cells by antiserum to RT. Its peptide map was nearly identical to that of virion p80(pol). Pulse-chase studies showed that Pr80(pol), Pr125(pol), and Pr135(pol) were stable polypeptides, whereas Pr200(gag-pol) and Pr145(pol) were unstable precursors. Pulse-chase studies with the protein synthesis inhibitor, cycloheximide, showed that the processing of Pr200(gag-pol) occurred for a short time in the absence of protein synthesis.
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PMID:Biosynthesis of reverse transcriptase from Rauscher murine leukemia virus by synthesis and cleavage of a gag-pol read-through viral precursor polyprotein. 7 22

beta-Lapachone is a naturally occuring compound that can be isolated from a number of tropical trees. It is shown to be a potent inhibitor of reverse transcriptase activity from both avian myeloblastosis virus and Rauscher murine leukaemia virus. In addition, it affects eukaryotic DNA-dependent DNA polymerase-alpha activity: 50% inhibition is reached in 60-min incubation time by about 8 micron beta-lapachone. Enzyme activity is inhibited irrespective of the purity of the enzyme used or of the amount or type of template/primer or substrate present. The inhibitory effect of the drug is only observed in the presence of dithiothreitol. The primary site of action of beta-lapachone appears to be the enzyme protein, as is also borne out by the specificity of its action. Eukaryotic DNA-dependent DNA polymerase-beta, prokaryotic DNA-dependent DNA polymerase I, several other nucleic acid polymerases and some completely unrelated enzymes are not affected. Reverse transcriptase and DNA-dependent DNA polymerase-alpha may be in someway related in possessing similarly exposed '--SH structures' in their active sites. beta-lapachone thus affords a novel means of studying such interrelationships and of further characterizing enzymes.
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PMID:beta-Lapachone, an inhibitor of oncornavirus reverse transcriptase and eukaryotic DNA polymerase-alpha. Inhibitory effect, thiol dependence and specificity. 7 23

Reverse transcriptase and p30 were purified from various retroviruses and the intra- and interspecific interaction between the two proteins were studied. The intraspecific complex stimulates [3H]TMP incorporation into (dT)12.(rA)n severalfold above that of the enzyme itself whereas DNA synthesis in the presence of the interspecific complex can stimulate DNA synthesis about 1.5-fold. The sedimentation rate value of the intraspecies complex varies between 12 and 16 S with an estimated molecular weight of 400,000. The molar ratio of p30:reverse transcriptase within the complex is 8:1. Both complexes can be dissociated into their original protein components by exposure to salt (kcl) solution, except that 0.3 M KCl will dissociate the interspecies complex whereas 0.8 M KCl is required for dissociation of the intraspecies complex. Competition studies in which an interspecies complex was exposed to p30 autologous to reverse transcriptase within the complex resulted in the displacement of the heterologous (p30) protein and the formation of a new intraspecific complex.
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PMID:Effect of RNA tumor virus-specific protein p30 on reverse transcriptase. Intraspecies and interspecies interaction between reverse transcriptase and p30. 8 36

Buffy coats from 31 patients with a diagnosis of leukemia and 16 normal donors were tested for the presence of a viral-like reverse transcriptase. Eighty-five percent of fresh leukemic buffy coats were positive. Also tested were spleens from 16 patients with hematological disorders and 5 spleens from patients without history of hematological malignancy. The 5 normal spleens were negative. Also negative were 4 spleens from patients with Hairy cell leukemia. From the remaining 12 spleens 7 were positive. Reverse transcriptase measurements can be used to distinguish leukemic from normal buffy coats.
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PMID:On the presence of reverse transcriptase in myelo- and lymphoproliferative disorders. 8 54


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