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:2.7.7.7 (DNA polymerase)
17,007 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two constituent protein domains of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase were expressed separately and purified to homogeneity. The N-terminal domain (p51) behaves as a monomeric protein exhibiting salt-sensitive DNA polymerase activity. The C-terminal domain (p15) on its own has no detectable RNase H activity. However, the combination of both isolated p51 and p15 in vitro leads to reconstitution of RNase H activity on a defined substrate. These results demonstrate that domains of HIV-1 reverse transcriptase are functionally interdependent to a much higher degree than in the case of reverse transcriptase from Moloney murine leukemia virus.
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PMID:Reconstitution in vitro of RNase H activity by using purified N-terminal and C-terminal domains of human immunodeficiency virus type 1 reverse transcriptase. 170 27

Screening of pharmacologically acceptable prototype compounds has recently led to the discovery of a series of ultraselective inhibitors of human immunodeficiency virus (HIV)-1 replication, the tetrahydroimidazo[4,5,1-jk] [1,4]-benzodiazepin-2(1H)-one and -thione (TIBO) derivatives. The TIBO compounds completely suppress the formation of proviral DNA in acutely infected cells, as revealed by polymerase chain reaction (PCR) analysis. TIBO derivatives are inhibitory to the reverse transcriptase (RT) of HIV-1 but not that of HIV-2 or other retroviruses. The inhibition is most effective with poly(C)-oligo(dG) as the template/primer, and it is selectively directed against the RNA-dependent DNA polymerase activity and not the accompanying DNA-dependent DNA polymerase and ribonuclease H activity of HIV-1 RT. Kinetic studies point to an uncompetitive inhibition with regard to the template/primer. TIBO compounds are active against HIV-1 replication through a unique interaction with HIV-1 RT. The experimental data indicate the existence of a target on HIV-1 RT that is responsible for the inhibition of replication and a mode of action unrelated to that of previously studied RT inhibitors.
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PMID:An antiviral target on reverse transcriptase of human immunodeficiency virus type 1 revealed by tetrahydroimidazo-[4,5,1-jk] [1,4]benzodiazepin-2 (1H)-one and -thione derivatives. 170 38

9-(2-Phosphonylmethoxyethyl)adenine (PMEA) is a potent and selective inhibitor of retrovirus (i.e., human immunodeficiency virus) replication in vitro and in vivo. Uptake of PMEA by human MT-4 cells and subsequent conversion to the mono- and diphosphorylated metabolites (PMEAp and PMEApp) are dose-dependent and occur proportionally with the initial extracellular PMEA concentrations. Adenylate kinase is unable to phosphorylate PMEA. However, 5-phosphoribosyl-1-pyrophosphate synthetase directly converts PMEA to PMEApp with a Km of 1.47 mM and a Vmax that is 150-fold lower than the Vmax for AMP. ATPase, 5'-phosphodiesterase, and nucleoside diphosphate kinase are able to dephosphorylate PMEApp to PMEAp, albeit to a much lower extent than the dephosphorylation of ATP. PMEApp has a relatively long intracellular half-life (16-18 hr) and has a much higher affinity for the human immunodeficiency virus-specified reverse transcriptase than for the cellular DNA polymerase alpha (Ki/Km: 0.01 and 0.60, respectively). PMEApp is at least as potent an inhibitor of human immunodeficiency virus reverse transcriptase as 2',3'-dideoxyadenosine 5'-triphosphate. Being an alternative substrate to dATP, PMEApp acts as a potent DNA chain terminator, and this may explain its anti-retrovirus activity.
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PMID:Intracellular metabolism and mechanism of anti-retrovirus action of 9-(2-phosphonylmethoxyethyl)adenine, a potent anti-human immunodeficiency virus compound. 170 39

We studied the effect of the natural marine substance illimaquinone on the catalytic activities of reverse transcriptase from human immunodeficiency virus type 1. Illimaquinone inhibited the RNase H activity of the enzyme at concentrations of 5 to 10 microgram/ml, whereas RNA-dependent DNA polymerase and DNA-dependent DNA polymerase activities were considerably less susceptible to this inhibition. Two synthetic derivatives of illimaquinone, in which the 6'-hydroxyl group at the ortho position to one of carbonyl groups of the quinone ring was modified, proved ineffective in inhibiting the human immunodeficiency virus type 1 reverse transcriptase RNase H function, suggesting involvement of the 6'-hydroxyl group in blocking the enzymatic activity.
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PMID:Illimaquinone, a selective inhibitor of the RNase H activity of human immunodeficiency virus type 1 reverse transcriptase. 170 12

Digallic acid (gallic acid 5,6-dihydroxy-3-carboxyphenyl ester) [4] was found to be a potent inhibitor of the activities of the reverse transcriptases from murine leukemia virus (MLV) and human immunodeficiency virus (HIV). Under the reaction conditions specified for each of MLV and HIV reverse transcriptases, both enzymes were inhibited by approximately 90% in the presence of 0.5 micrograms/ml digallic acid. Under the same conditions, however, gallic acid had no effect on the reverse transcriptase activity. The mode of the inhibition by digallic acid was partially competitive with respect to the template.primer, (rA)n.(dT)12-18', and noncompetitive to the triphosphate substrate, dTTP. The Ki value of digallic acid for HIV-reverse transcriptase was determined to be 0.58 microM. Examination of several derivatives of digallic acid have shown that all three hydroxyl groups at the 3, 4, and 5 positions seem to be required for the inhibitory activity of these compounds. Besides reverse transcriptase, DNA polymerases alpha and beta were moderately inhibited by digallic acid, whereas DNA polymerase gamma, terminal deoxynucleotidyltransferase, and E. coli DNA polymerase I were virtually insensitive to inhibition by this compound.
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PMID:Differential inhibition of reverse transcriptase and various DNA polymerases by digallic acid and its derivatives. 170 74

3'-Azido-2',3'-dideoxy-5-methylcytidine (CS-92, AzddMeC) is an antiviral nucleoside analogue structurally related to 3'-azido-3'-deoxythymidine (AZT). CS-92 is a potent and selective inhibitor of HIV-1 reverse transcriptase and HIV-1 replication in human lymphocytes and macrophages. The EC50 for CS-92 in HIV-1-infected human PBM cells was 0.09 microM. In HIV-1-infected human macrophages, the EC50 was 0.006 microM. This compound was also effective against human immunodeficiency virus type 2 in lymphocytes. The replication of Friend murine virus was only weakly inhibited, and no effect was observed against herpes simplex virus type 1 and type 2 and coxsackievirus B4. CS-92 was not toxic to PBM or Vero cells when tested up to 200 microM and was, furthermore, at least 40 times less toxic to granulocyte-macrophage and erythroid precursor cells in vitro than was AZT. The interaction of the 5'-triphosphate of CS-92 with HIV-1 reverse transcriptase indicated competitive inhibition (the inhibition constant, Kis, was 0.0093 microM) with a 30-fold greater affinity for CS-92-TP than for ddCTP. CS-92-TP inhibited HIV-1 reverse transcriptase by 50% at a concentration 6,000-fold lower than that which was required for a similar inhibition of DNA polymerase alpha. Pharmacokinetic studies showed that CS-92 was not deaminated to AZT in rats, but this compound was found to have a half-life of 2.7 hours. In rhesus monkeys, however, a compound with a retention time and ultraviolet spectra characteristics similar to AZT was detected. The mean half-life in rhesus monkeys for CS-92 was 1.52 and 1.74 h after intravenous and oral administration, respectively, and the oral bioavailability was about 21 percent. Additional preclinical studies with CS-92 will determine the ultimate utility of this antiviral agent for the treatment of HIV-1 infections.
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PMID:Antiretroviral activity, biochemistry, and pharmacokinetics of 3'-azido-2',3'-dideoxy-5-methylcytidine. 170 74

The enzyme reverse transcriptase (RT) is crucial in the early steps of the life cycle of retroviruses. We have expressed in bacteria the RTs from human immunodeficiency viruses (HIV) types 1 and 2 in order to study the structural-functional relationships of these two multifunctional enzymes that share a relatively high degree of amino acid sequence homology. For comparison purposes, we have analyzed several catalytic functions of both enzymes. The two HIV RTs show a high similarity in many aspects studied but exhibit profound differences in several other properties. For instance, the specific RNase H activity of HIV-2 RT is about 10 times lower than the corresponding activity of HIV-1 RT. There are also significant dissimilarities between some of the apparent Km values calculated for the DNA polymerizing functions of both enzymes. Furthermore, the heat stability of the DNA polymerizing activity of HIV-2 RT is about 15-fold higher than that of HIV-1 RT. On the other hand, the susceptibility of the RNase H activities of the two enzymes to heat inactivation was found to be similar. Other treatments also enable discrimination between the RNase H and DNA polymerizing catalytic properties of the two enzymes (although both reverse transcriptases respond similarily). Thus, the RNase H activity was inactivated by N-ethylmaleimide, suggesting the possible involvement of cysteine residues in performing this activity, whereas the DNA polymerizing functions of the two enzymes were fully resistant to this chemical modification. The zinc chelator 1,10-phenanthroline affected the DNA polymerase activities of both enzymes to a significantly higher extent than the RNase H activity. In all, the two HIV RTs were shown to be substantially different one from the other in several of their properties and also distinct from other RTs thus far studied.
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PMID:Catalytic properties of the reverse transcriptases of human immunodeficiency viruses type 1 and type 2. 170 12

A new class of compounds, 9-[(2RS)-3-fluoro-2-phosphonylmethoxypropyl] [(RS)-FPMP] derivatives of purines, is described that has selective activity against a broad spectrum of retroviruses [including human immunodeficiency virus type 1 (HIV-1) and type 2 (HIV-2)] but not other RNA or DNA viruses. This activity spectrum is completely different from that of the parental compounds, 9-[(2S)-3-hydroxy-2-phosphonylmethoxypropyl] [(S)-HPMP] derivatives of purines, which are active against a broad range of DNA viruses. The racemic (RS)-FPMP derivatives of adenine and 2,6-diaminopurine, termed (RS)-FPMPA and (RS)-FPMPDAP, respectively, are markedly more selective as in vitro antiretroviral agents than their 9-(2-phosphonylmethoxyethyl) (PME) counterparts, PMEA and PMEDAP. Also, (RS)-FPMPA and (RS)-FPMPDAP have a substantially higher therapeutic index in mice in inhibiting Moloney murine sarcoma virus-induced tumor formation and associated death and are markedly less inhibitory to human bone marrow cells than PMEA and PMEDAP. The diphosphate derivative of (RS)-FPMPA [(RS)-FPMPApp] is a potent and selective inhibitor of HIV-1 reverse transcriptase but not of HSV-1 DNA polymerase or DNA polymerase alpha. (RS)-FPMPApp, akin to PMEA diphosphate (PMEApp), acts as a DNA chain terminator. The DNA chain-terminating properties of PMEApp and (RS)-FPMPApp seem to be a prerequisite for acyclic nucleoside phosphonates to exhibit antiretrovirus (i.e., anti-HIV) activity.
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PMID:9-[(2RS)-3-fluoro-2-phosphonylmethoxypropyl] derivatives of purines: a class of highly selective antiretroviral agents in vitro and in vivo. 171 Dec 14

We have examined the properties of reverse transcriptases (RTs) required for strand transfer synthesis on poly(rA). In this process, a primer is elongated on one template and then switches to other templates for additional elongation until it is much longer than the templates on which it was made. Models of retrovirus replication require the RT to catalyze two distinct strand transfers. Additionally, they propose that the RT ribonuclease H (RNase H) activity is involved in both transfers. RTs from human immunodeficiency virus (HIV), avian myeloblastosis virus, and murine leukemia virus differ in molecular mass and subunit composition. However, they all catalyzed strand transfer synthesis on (rA)300, generating characteristically long products. An RNase H-deficient enzyme, HIV-RTRD, catalyzed strand transfer synthesis to the same degree as native HIV-RT, indicating that a functional RNase H activity is not required. Additionally, N-ethylmaleimide, which inhibits RNase H but not polymerase activity of HIV-RT, did not diminish strand transfer synthesis. Highly processive DNA synthesis by each RT was found to be required for the strand transfer reaction. RNase H- murine leukemic virus RT has a structural modification that not only eradicates RNase H, but also makes the polymerase much less processive for DNA synthesis. However, conditions that allow this modified enzyme to bind repeatedly to the same primer during synthesis, i.e. conditions that simulate higher processivity, allow strand transfer synthesis. Catalysis of strand transfer synthesis is not a property of all DNA polymerases, since the Klenow fragment of Escherichia coli DNA polymerase I is unable to catalyze this reaction even if high processivity is simulated. These results suggest that strand transfer synthesis relies on an unidentified functional activity present in RTs.
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PMID:Requirements for the catalysis of strand transfer synthesis by retroviral DNA polymerases. 171 74

The human immunodeficiency virus 1 (HIV-1) reverse transcriptase (RT) is a protein of 66 kDa, p66, which contains two domains, an amino-terminal DNA polymerase and an RNase H at the carboxy terminus of the molecule. In order to characterize the mode of action of the RNase H, two previously described mutant enzymes were used, with substitutions in the highly conserved histidine 539, which was mutated to the neutral amino acid asparagine and to the negatively charged aspartate. The purified wild-type (wt) and mutant (mt) enzyme activities are analyzed here using RNA-DNA hybrids consisting of in vitro transcribed RNA that harbors the polypurine tract (PPT) from HIV-1 and DNA oligonucleotides complementary to the PPT or to other regions of the RNA. Analysis of the radioactively labeled RNA of these model hybrids after RNase H treatment indicates that both, wt and mt enzymes, are capable of cleaving the RNA in an endonucleolytic manner. The mt enzymes exhibit a severely reduced exonuclease activity. They are more sensitive towards salt and competition with excess of unlabeled hybrid, suggesting a reduced substrate binding affinity. DNA elongation by the RT is coupled with RNA hydrolysis by the 3'-5' exonuclease of the wt RNase H. The RNase Hmt of the mt enzymes, however, does not exhibit such processive 3'-5' exonuclease activity during DNA synthesis but gives rise to sporadic endonucleolytic cuts, whereas the RT is not affected. The endonuclease activities of the RNase H mt enzymes exhibit cleavage preferences in the absence or presence of DNA synthesis different from those of the wt enzyme. They cannot recognize specific sequences required to generate a PPT-primer and therefore cannot initiate plus-strand DNA synthesis in vitro at the 3' end of the PPT, which is essential for viral replication.
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PMID:Mutations of a conserved residue within HIV-1 ribonuclease H affect its exo- and endonuclease activities. 171 5


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