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:2.7.7.49 (reverse transcriptase)
31,746 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Four isomeric benzo[a]pyrene-deoxyadenosine adducts, corresponding to the products of trans opening of the epoxide ring in the four configurationally isomeric benzo[a]pyrene dihydrodiol epoxides by the amino group of deoxyadenosine, were separately introduced into each of two 16-mer sequence contexts. The sequences were from the supF gene, and the site of the adducted adenine was known, for some hydrocarbon dihydrodiol epoxides, to be a hotspot for mutation in Context I and a coldspot for mutation in Context II. Using primers complementary to the 3' ends of these oligonucleotides, the abilities of several polymerases to replicate these templates in vitro were investigated. Each adduct proved to be an effective block to primer extension such that only with high concentrations of exo- Klenow fragment was any bypass of adducts seen. DNA polymerase alpha and HIV-1 reverse transcriptase were blocked 3' to the adduct when the configuration at C10 of the hdyrocarbon was S, and some introduction of thymine opposite the adenine adduct was seen with the R configuration. Incorporation of a nucleotide opposite the adduct occurred more readily with Sequenase and the Klenow fragment, and the mutagenic introduction of adenine was apparent in most cases. This corresponded to the A-->T transversions frequently seen in mutation studies with hydrocarbon dihydrodiol epoxides that react extensively with adenine in DNA. Overall, it was clear that sequence context, adduct stereochemistry, and the choice of polymerase all influenced the polymerization reaction. With these in vitro systems, no major differences correlating with the differing tumorigenicities of the isomeric dihydrodiol epoxides or with the hotspot or coldspot nature of the sequences were detected.
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PMID:Primer extension by various polymerases using oligonucleotide templates containing stereoisomeric benzo[a]pyrene-deoxyadenosine adducts. 752 75

L-beta-Deoxythymidine (L-dT), the optical enantiomer of D-beta-deoxythymidine (D-dT), and L-enantiomers of nucleoside analogs, such as 5-iodo-2'-deoxy-L-uridine (L-IdU) and E-5-(2-bromovinyl)-2'-deoxy-L-uridine (L-BVdU), are not recognized in vitro by human cytosolic thymidine kinase (TK), but are phosphorylated by herpes simplex virus type 1 (HSV-1) TK and inhibit HSV-1 proliferation in infected cells. Here we report that: (i) L-dT is selectively phosphorylated in vivo to L-dTMP by HSV-1 TK and L-dTMP is further phosphorylated to the di- and triphosphate forms by non-stereospecific cellular kinases; (ii) L-dTTP not only inhibits HSV-1 DNA polymerase in vitro, but also human DNA polymerase alpha, gamma, delta and epsilon, human immunodeficiency virus reverse transcriptase (HIV-1 RT), Escherichia coli DNA polymerase 1 and calf thymus terminal transferase, although DNA polymerase beta was resistant; (iii) whereas DNA polymerase beta, gamma, delta and epsilon are unable to utilize L-dTTP as a substrate, the other DNA polymerases clearly incorporate at least one L-dTMP residue, with DNA polymerase alpha and HIV-1 RT able to further elongate the DNA chain by catalyzing the formation of the phosphodiester bond between the incorporated L-dTMP and an incoming L-dTTP; (iv) incorporated L-nucleotides at the 3'-OH terminus make DNA more resistant to 3'-->5' exonucleases. In conclusion, our results suggest a possible mechanism for the inhibition of viral proliferation by L-nucleosides.
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PMID:Stereospecificity of human DNA polymerases alpha, beta, gamma, delta and epsilon, HIV-reverse transcriptase, HSV-1 DNA polymerase, calf thymus terminal transferase and Escherichia coli DNA polymerase I in recognizing D- and L-thymidine 5'-triphosphate as substrate. 754 86

3'-Azido-2',3'-dideoxy-5-iodouridine (AzIdUrd) and 3'-azido-2',3'-dideoxy-5-bromouridine (AzBdUrd), previously shown to be potent and selective inhibitors of human immunodeficiency virus replication in vitro were minimally toxic to the uninfected human lymphoid cell line H9 (IC50 = 197 and 590 microM, respectively). Both compounds strongly inhibited the incorporation of [3H]thymidine but not [3H]deoxyadenosine into DNA, and we observed no significant inhibition of [3H]uridine incorporation into RNA or [3H]amino acid incorporation into protein. Exposure of H9 cells to AzIdUrd or AzBdUrd (100 microM, 24 hr) and pulse-labeling with [3H]thymidine resulted in approximately 80% reduction in levels of tritiated dTMP, dTDP, and dTTP relative to control. [125I]AzIdUrd was phosphorylated rapidly in H9 cells with the monophosphate accounting for over 90% of total soluble radioactivity. A relatively low but stable level of AzIdUTP was maintained over a 12-hr period. [125I]AzIdUrd was phosphorylated by a cell free extract of H9 cells at a rate approximately three times that of thymidine and its phosphorylation was inhibited by excess thymidine. AzIdUrd was found to be a competitive inhibitor of cytosolic thymidine kinase with a Ki of 2.63 microM and AzIdUMP a weak competitive inhibitor of thymidylate kinase with a Ki of 55.3 microM. Both AzIdUTP and AzBdUTP were potent competitive inhibitors of HIV-1 reverse transcriptase (Ki = 0.028 and 0.043 microM, respectively) and relatively poor inhibitors of H9 cell DNA polymerase alpha (Ki = 42.0 and 42.7 microM, respectively). Thus, the high therapeutic index of these compounds is due to the sensitivity of the viral reverse transcriptase, coupled with the relative insensitivity of the host cell DNA polymerase alpha.
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PMID:Metabolism and mode of selective inhibition of human immunodeficiency virus replication by 3'-azido-2',3'-dideoxy-5-iodouridine and 3'-azido-2',3'-dideoxy-5-bromouridine. 767 40

In the search for 1-[(2-hydroxyethoxy)methyl]-6-(phenylthio)thymine derivatives, we have found 6-benzyl-1-(ethoxymethyl)-5-isopropyl-uracil (MKC-442) to be a highly potent and selective inhibitor of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT). The IC50 value of MKC-442 for HIV-1 RT was 8 nM. MKC-442 did not inhibit HIV-1 RNase H, other RTs, or DNA polymerase alpha. Because its inhibitory pattern showed noncompetitive inhibition with regard to nucleotide substrates, its mode of action was considered to be allosteric inhibition. From the results of combination studies, MKC-442 was found to produce synergistic inhibition of HIV-1 RT with 3'-azido-2',3'-dideoxythymidine (AZT) 5'-triphosphate (AZT.TP). The dose of AZT.TP required for 50% inhibition was reduced to one tenth of control in the presence of a half dose of MKC-442. Although other allosteric inhibitors (Nevirapine, L-696,229, and R82,913) had the same specificity for enzyme inhibition, they did not show synergism with AZT.TP in the combination index and synergy plot analyses. Synergistic inhibition of HIV-1 replication by MKC-442 and AZT has also been observed in HIV-1-infected MT-4 cells. These results suggest that MKC-442 is a unique inhibitor of HIV-1 RT, and combination therapy with MKC-442 and AZT could be advantageous in the treatment of acquired immune deficiency syndrome.
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PMID:Selective and synergistic inhibition of human immunodeficiency virus type 1 reverse transcriptase by a non-nucleoside inhibitor, MKC-442. 769 70

The bis(monosuccinimide) derivative of p,p'-bis(2-aminoethyl)diphenyl-C60 (compound 1), prepared by the fulleroid route, is active against human immunodeficiency virus type 1 (HIV-1) and HIV-2 (50% effective concentration [EC50] averaging approximately 6 microM) in acutely or chronically infected human lymphocytes and is active in vitro against 3'-azido-3'-deoxythymidine-resistant HIV-1 (EC50, approximately 3 microM). The virucidal properties of compound 1 were confirmed by virus inactivation assays. Compound 1 was noncytotoxic up to 100 microM in peripheral blood mononuclear cells and H9, Vero, and CEM cells. In cell-free assays, whereas the fullerene showed comparable activity against HIV-1 reverse transcriptase and DNA polymerase alpha (50% inhibitory concentration of approximately 5 microM), it demonstrated selective activity against HIV-1 protease.
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PMID:Synthesis and virucidal activity of a water-soluble, configurationally stable, derivatized C60 fullerene. 821 89

Nickel is a genotoxic carcinogen. However, the mechanisms of nickel-induced genotoxicity are not well understood. We have investigated the effects of Ni2+ ions on DNA polymerase activity and the fidelity of DNA replication in vitro. The effect of Ni2+ on different DNA polymerases is quite variable. The amount of enzyme inhibition and degree of alteration in replication fidelity induced by Ni2+ are dependent both on the polymerase and its associated 3'-5' exonuclease activity. Some polymerases, such as E. coli DNA polymerase I, AMV reverse transcriptase and human DNA polymerase alpha, can utilize Ni2+ as a weak substitute for Mg2+ during DNA replication. Other polymerases are very sensitive to inhibition by Ni2+ and the IC50 can vary by an order of magnitude. T4 polymerase is relatively insensitive to inhibition by Ni2+, although the sensitivity is enhanced in the absence of added Mg2+, and Ni preferentially inhibits the 3'-5' exonuclease function of T7 DNA polymerase. The fidelity and processivity of DNA polymerases may be either increased or decreased by Ni ions in a polymerase dependent manner. The inhibition DNA polymerase activity and altered replication fidelity may contribute significantly to Ni-induced mutagenesis and genotoxicity in vivo.
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PMID:Effects of nickel ions on polymerase activity and fidelity during DNA replication in vitro. 840 77

Quinoxapeptin A and B are novel chromodepsipeptides which were isolated from a nocardioform actinomycete with indeterminant morphology. Quinoxapeptins A and B are potent inhibitors of HIV-1 and HIV-2 reverse transcriptase and almost equally active against two single mutants forms as well as a double mutant form of HIV-1 reverse transcriptase. Quinoxapeptin A and B are specific inhibitors of HIV-1 and HIV-2 reverse transcriptase because they did not inhibit human DNA polymerase alpha, beta, gamma and delta. Quinoxapeptin A and B are structurally similar to luzopeptin A which was also active against HIV-1 and HIV-2 reverse transcriptase.
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PMID:Quinoxapeptins: novel chromodepsipeptide inhibitors of HIV-1 and HIV-2 reverse transcriptase. I. The producing organism and biological activity. 862 40

Boronated oligonucleotides are potential candidates for boron neutron capture therapy, antisense technology, and as tools in molecular biology. The biological properties of dodecathymidylic acids containing one or more 5-(o-carboran-1-yl)-2'-deoxyuridine residues at different locations within the oligonucleotide chain were studied. 5-(o-Carboran-1-yl)-2'-deoxyuridine containing oligonucleotides manifested marked increased lipophilicity and resistance to 3'- or 5'-phosphodiesterases compared to the corresponding unmodified oligomer. They were substrates for T4 polynucleotide kinase and primers for Escherichia coli polymerase I and human immunodeficiency virus type 1 reverse transcriptase but not for human DNA polymerase alpha and beta. They also formed heteroduplexes that were substrates for E. coli RNase H, an essential property for antisense technology. These studies indicate that the carboranyl-containing oligonucleotides have desirable properties that need to be exploited further in the design of novel biopharmaceuticals.
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PMID:Carboranyl oligonucleotides. 3. Biochemical properties of oligonucleotides containing 5-(o-carboranyl-1-yl)-2'-deoxyuridine. 863 34

Several 2'-deoxythymidine 5'-triphosphate and 3'-azido-2', 3'-dideoxythymidine 5'-triphosphate analogs containing a hydrophobic phosphonate group instead of the gamma-phosphate were synthesized and evaluated as substrates for human immunodeficiency virus (HIV) and avian myeloblastosis virus reverse transcriptases, human placental DNA polymerases alpha and beta, and calf thymus terminal deoxynucleotidyl transferase. They were efficiently incorporated into the DNA chain by the retroviral enzymes but were not utilized by the mammalian ones. Also, some gamma-ester and gamma-amide derivatives of dTTP and 3'-azido-2',3'-dideoxythymidine 5'-triphosphate (AZTTP) were synthesized and studied. They proved to be substrates for both the retroviral and mammalian enzymes under study. The Km values for incorporation of the dTTP derivatives into the DNA chain were close to those for dTTP and AZTTP. The Km for the AZTTP derivatives were one order of magnitude greater than those for dTTP and AZTTP. The results obtained indicate that HIV and avian myeloblastosis virus reverse transcriptases have no sterical obstacles for binding the triphosphate fragment bearing a bulky substituent at the gamma-position. Modification of the gamma-phosphate in AZTTP increased the selectivity of HIV reverse transcriptase inhibition versus DNA polymerase alpha. gamma-Methylphosphonate and gamma-phenylphosphonate were dephosphorylated in human serum much less rapidly than AZTTP. Besides, they were shown to be markedly more hydrophobic than AZTTP. Thus, replacement of the gamma-phosphate in AZTTP with gamma-phosphonate markedly alters its substrate properties toward some cellular DNA polymerases and blood dephosphorylating enzymes but does not change its substrate activity with respect to HIV reverse transcriptase.
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PMID:Gamma-phosphate-substituted 2'-deoxynucleoside 5'-triphosphates as substrates for DNA polymerases. 879 94

In the search for effective antiviral agents, we have found 4-(2, 6-dichlorophenyl)-1, 2, 5-thiadiazol-3-yl-N-methyl, N-ethylcarbamate (RD4-2025) to be a highly potent and selective inhibitor of human immunodeficiency virus type 1 (HIV-1) in vitro. The 50% effective concentration of RD4-2025 for HIV-1-induced cytopathic effect in MT-4 cells was 37 nM, yet no antiviral activity was observed against HIV-2. In HIV-1 reverse transcriptase (RT) assays, RD4-2025 inhibited both RNA-dependent and DNA-dependent DNA polymerase activities of a recombinant HIV-1 RT with 50% inhibitory concentrations of 0.11 and 3.5 microM, respectively. However, the compound did not affect the activity of human DNA polymerase alpha. Kinetic studies revealed that the inhibition was noncompetitive with respect to dGTP as the substrate and poly(C)/(dG) 12-18 as the template/primer. These results were in accordance with those of nonnucleoside RT inhibitors (NNRTIs), such as R89439 (an alpha-anilinophenylacetamide derivative) and nevirapine, indicating that RD4-2025 also belongs to the family of NNRTIs.
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PMID:Inhibitory effect of 4-(2, 6-dichlorophenyl)-1, 2, 5-thiadiazol-3-yl-N-methyl, N-ethylcarbamate on replication of human immunodeficiency virus type 1 and the mechanism of action. 879 26


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