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:3.1.26.4 (RNase H)
2,751 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The quinoline U-78036 represents a new class of non-nucleoside human immunodeficiency virus (HIV)-1 reverse transcriptase inhibitors. The agent possesses excellent antiviral activity at nontoxic doses in HIV-1-infected lymphocytes grown in tissue culture. Enzymatic kinetic studies of the HIV-1 reverse transcriptase (RT)-catalyzed RNA-directed DNA polymerase function were carried out in order to determine whether the inhibitor interacts with the template-primer or deoxyribonucleotide triphosphate (dNTP) binding sites of the polymerase. The data were analyzed using steady-state or Briggs-Haldane kinetics assuming that the template-primer binds to the enzyme first followed by the dNTP and that the polymerase functions processively. The calculated rate constants are in agreement with this model. The results show that the inhibitor acts as a mixed to noncompetitive inhibitor with respect to both the template-primer and the dNTP binding sites of the enzyme. Hence, U-78036 inhibits the RNA-directed DNA polymerase activity of RT by interacting with a site distinct from the template-primer and dNTP binding sites. Moreover, the potency of U-78036 is dependent on the base composition of the template-primer. The equilibrium constants for various enzyme-substrate-inhibitor complexes were at least seven times lower for the poly(rC).(dG)10-catalyzed system than the one catalyzed by poly(rA).(dT)10. In addition, the inhibitor does not impair the DNA-dependent DNA polymerase activity and the RNase H function of HIV-1 RT nor does it inhibit the RNA-directed DNA polymerase activity of the HIV-2, avian myoblastoma virus, and murine leukemia virus RT enzymes.
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PMID:The quinoline U-78036 is a potent inhibitor of HIV-1 reverse transcriptase. 768 7

Replication of hepadnaviruses involves reverse transcription of an intermediate RNA molecule. It is generally accepted that this replication scheme is carried out by a virally encoded, multifunctional polymerase which has DNA-dependent DNA polymerase, reverse transcriptase, and RNase H activities. Biochemical studies of the polymerase protein(s) have been limited by the inability to purify useful quantities of functional enzyme from virus particles and, until recently, to express enzymatically active polymerase proteins in heterologous systems. An activity gel assay which detects in situ catalytic activities of DNA polymerases after electrophoresis in partially denaturing polyacrylamide gels was used by M.R. Bavand and O. Laub (J. Virol. 62:626-628, 1988) to show the presence of DNA- and RNA-dependent DNA polymerase activities associated with hepatitis B virus particles produced in vitro. This assay has provided the only means by which hepadnavirus polymerase proteins have been detected in association with enzymatic activities. Since conventional methods have not allowed purification of useful quantities of enzymatically active polymerase protein(s), we have devised a protocol for purifying large quantities of duck hepatitis B virus (DHBV) core particles to near homogeneity. These immature virus particles contain DNA- and RNA-dependent DNA polymerase activities, as shown in the endogenous DNA polymerase assay. We have used the activity gel assay to detect multiple DNA- and RNA-dependent DNA polymerase proteins associated with these purified DHBV core particles. These enzymatically active proteins appear larger than, approximately the same size as, and smaller than an unmodified DHBV polymerase protein predicted from the polymerase open reading frame. This is the first report of the detection of active hepadnavirus core-associated DNA polymerase proteins derived from a natural host.
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PMID:Detection of DNA polymerase activities associated with purified duck hepatitis B virus core particles by using an activity gel assay. 841 59

The replication of the hepatitis B viral DNA genome proceeds through a pregenomic RNA intermediate. This pregenomic RNA subsequently serves as the template for the formation of the viral DNA by the reverse transcriptase activity of the viral P gene product. The P gene product is believed to be a multifunctional enzyme with DNA-dependent DNA polymerase, RNA-dependent DNA polymerase, and RNase H activities. Detailed biochemical studies of this protein have not been performed because of the inability to obtain sufficient amounts of the enzyme from the virus and by the inability to produce the enzyme in heterologous expression systems. The RNase H activity is essential for viral replication and is believed to be responsible for the degradation of the RNA pregenomic intermediate as well as for generating the short RNA primer that is required for DNA second strand synthesis. We have assembled an expression vector which directs the synthesis of a protein that corresponds to the putative RNase H domain of the P gene product and having a carboxyl-terminal polyhistidine tag to facilitate purification. The protein has been expressed in Escherichia coli and purified to yield 1-2 mg of protein/liter of culture. This protein has RNase H activity as defined by its ability to degrade the RNA component of RNA-DNA hybrids but not the DNA component. The RNase H has a basic optimum pH, is active only in the presence of reducing agents, and is dependent on the presence of divalent cations, with magnesium being preferred over manganese.
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PMID:Expression, purification, and characterization of an active RNase H domain of the hepatitis B viral polymerase. 895 90

HIV-1 reverse transcriptase (RT) is multifunctional, with RNA-dependent DNA polymerase (RDDP), DNA-dependent DNA polymerase (DDDP), and ribonuclease H (RNase H) activities. N-(4-tert-Butylbenzoyl)-2-hydroxy-1-naphthaldehyde hydrazone (BBNH) inhibited both the polymerase and the RNase H activities of HIV-1 RT in vitro. IC50 values for inhibition of RDDP were 0.8-3.4 microM, depending on the template/primer (T/P) used in the assay. The IC50 for DDDP inhibition was about 12 microM, while that for inhibition of RNase H was 3.5 microM. EC50 for inhibition of HIV-1 replication in cord blood mononuclear cells was 1.5 microM. BBNH inhibition of RNase H in vitro was time-dependent, whereas inhibition of RT polymerase activities was immediate. BBNH was a linear mixed-type inhibitor of RT RDDP activity with respect to both T/P and to dNTP, whereas BBNH inhibition of RT RNase H activity was linear competitive. Protection experiments using an azidonevirapine photolabel showed that BBNH binds to the non-nucleoside RT inhibitor (NNRTI) binding pocket. Importantly, the compound inhibited recombinant RT containing mutations associated with high-level resistance to other NNRTI. While BBNH did not inhibit the DNA polymerase activities of other retroviral reverse transcriptases and DNA polymerases, the compound inhibited Escherichia coli RNase HI and the RNase H activity of murine leukemia virus RT. BBNH also inhibited HIV-1 RT RNase H in the presence of high concentrations of other non-nucleoside inhibitors with higher affinities for the NNRTI binding pocket, and of RT in which the NNRTI binding pocket had been irreversibly blocked by the azidonevirapine photolabel. We conclude that BBNH may therefore bind to two sites on HIV-1 RT. One site is the polymerase non-nucleoside inhibitor binding site and the second may be located in the RNase H domain. BBNH is therefore a promising lead compound for the development of multisite inhibitors of HIV-1 RT.
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PMID:Inhibition of the ribonuclease H and DNA polymerase activities of HIV-1 reverse transcriptase by N-(4-tert-butylbenzoyl)-2-hydroxy-1-naphthaldehyde hydrazone. 911 94

We have constructed a plasmid that induces in bacteria the synthesis of an enzymically active reverse transcriptase (RT) of mouse mammary tumour virus (MMTV), a retrovirus with a typical B-type morphology. The highest catalytic activity was detected only when 27 residues from the C-terminus of the protease were included in the N-terminus of the recombinant RT, after an extra deoxyadenosine was added between the pro and pol genes to overcome the -1 frameshift event (which occurs naturally in virus-infected cells). The recombinant protein with a six-histidine tag was purified to homogeneity by a two-column purification procedure, Ni2+ nitriloacetic acid/agarose followed by carboxymethyl-Sepharose chromatography. Unlike most RTs, the purified MMTV RT is enzymically active as a monomer even after binding a DNA substrate. Like all RTs studied, the recombinant MMTV RT possesses RNA-dependent and DNA-dependent DNA polymerase activities as well as RNase H activity, all of which show a preference for Mg2+ over Mn2+ ions. Other features of these enzymic activities, such as extension of DNA primers, processivity of DNA synthesis, pH dependence, steady-state kinetic constants, effects of Na+ or K+ ions and sensitivity to a thiol-specific reagent and to a zinc chelator, have been evaluated. The catalytic properties of MMTV RT were compared with those of the well-studied RT of HIV-1, the causative agent of AIDS. Interestingly, MMTV RT exhibits a high sensitivity to nucleoside triphosphate analogues (which are known to be potent inhibitors of HIV RTs and are being used as the major anti-AIDS drugs), as high as that of HIV-1 and HIV-2 RTs. Furthermore the recombinant MMTV RT shows a processivity of DNA synthesis higher than that of HIV-1 RT.
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PMID:Reverse transcriptase of mouse mammary tumour virus: expression in bacteria, purification and biochemical characterization. 944 85

The hepadnavirus P gene product is a multifunctional protein with priming, DNA- and RNA-dependent DNA polymerase, and RNase H activities. Nested N- or C-terminal deletion mutations and deletions of domain(s) in human HBV polymerase have been made. Wild-type and deletion forms of MBP-fused HBV polymerase were expressed in E. coli, purified by amylose column chromatography, and the DNA-dependent DNA polymerase activities of the purified proteins were compared. Deletion of the terminal protein or spacer regions reduced enzyme activity to 70%, respectively. However, deletion of the RNase H domain affected polymerase activity more than that of the terminal protein or spacer region. The polymerase domain alone or the N-terminal deletion of the polymerase domain still exhibited enzymatic activity. In this report, it is demonstrated that the minimal domain for the polymerizing activity of the HBV polymerase is smaller than the polymerase domain.
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PMID:Hepatitis B virus: DNA polymerase activity of deletion mutants. 1020 76

We have expressed the recombinant reverse transcriptase (RT) of bovine leukemia virus (BLV) in bacteria. The gene encoding the RT was designed to start at its 5' end next to the last codon of the mature viral protease, namely the amino terminus of the RT matches the last 26 codons of the pro gene and is coded for by the pro reading frame. The RT sequence extends into the pol gene, utilizing the pol reading frame after overcoming the stop codon by adding an extra nucleotide (thus imitating the naturally occurring frameshift event). Hence we have generated a transframe polypeptide that is a 584-residues-long protein (see Rice, Stephens, Burny, and Gilden (1985) Virology 142, 357-377). This protein was partially purified after adding a six-histidine tag and studied biochemically testing a variety of parameters. The enzyme exhibits all activities typical of RTs, i.e., both RNA- and DNA-dependent DNA polymerase as well as a ribonuclease H (RNase H) activity. Unlike most RTs, the BLV RT is enzymatically active as a monomer even after binding a DNA substrate. The enzyme shows a preference for Mg2+ over Mn2+ in both its DNA polymerase and RNase H activities. BLV RT is relatively resistant to nucleoside triphosphate analogues, which are known to be potent inhibitors of other RTs such as that of HIV.
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PMID:Catalytic features of the recombinant reverse transcriptase of bovine leukemia virus expressed in bacteria. 1036 2

The physiological significance of the casein kinase II (CK-II)-mediated phosphorylation of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) on its three enzymatic activities [RNA-dependent DNA polymerase (RDDP), DNA-dependent DNA polymerase (DDDP) and ribonuclease H (RNase H)] was investigated in vitro. It was found that (i) the purified recombinant RT (rRT) functioned as an effective phosphate acceptor for CK-II; (ii) the RDDP, DDDP and RNase H activity of rRT was stimulated about 2.8-, 4.1- and 3.9-fold, respectively, after full phosphorylation by CK-II; and (iii) this stimulation was selectively inhibited by potent CK-II inhibitors, such as neocarzinostatin-chromophore (NCS-chrom) and three polyphenol-containing anti-oxidant compounds [quercetin, epigallocatechin gallate (EGCG) and 8-chloro-3',4',5,7-tetrahydroxyisoflavone (8C-3',4',5,7-THI)]. These results suggest that (i) CK-II may be responsible for activation of RT in HIV-1-infected cells; and (ii) the selective inhibition of CK-II-mediated activation of HIV-1 RT by potent CK-II inhibitors may be involved in the mechanism of their anti-HIV-1 effects at the cellular level.
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PMID:Casein kinase II (CK-II)-mediated stimulation of HIV-1 reverse transcriptase activity and characterization of selective inhibitors in vitro. 1054 69

Three new kaempferol glycosides, called crassirhizomosides A (1), B (2) and C (3), were isolated from the rhizome of Dryopteris crassirhizoma (Aspidiaceae), together with the known kaempferol glycoside, sutchuenoside A (4). The structures of 1-3 were determined as kaempferol 3-alpha-L-(2,4-di-O-acetyl)rhamnopyranoside-7-alpha-L-rhamnopyranoside, kaempferol 3-alpha-L-(3,4-di-O-acetyl)rhamnopyranoside, and kaempferol 3-alpha-L-(2,3-di-O-acetyl)rhamnopyranosside-7-alpha-L-rhamnopyranoside, respectively, by chemical and spectroscopic means. Inhibitory effects of 1-4 and kaempferol on human immunodeficiency virus reverse transcriptase-associated DNA polymerase (RNA-dependent DNA polymerase and DNA-dependent DNA polymerase) and RNase H activities were investigated.
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PMID:Kaempferol acetylrhamnosides from the rhizome of Dryopteris crassirhizoma and their inhibitory effects on three different activities of human immunodeficiency virus-1 reverse transcriptase. 1138 4

Retroelements are mobile genetic entities that replicate via reverse transcription of a template RNA. A key component to the life cycle of these elements is the enzyme reverse transcriptase (RT), which copies the single-stranded genomic RNA of the element into a linear double-stranded DNA that is ultimately integrated into the host genome by the element-encoded integrase. RT is a multifunctionnal enzyme which possesses RNA-dependent and DNA-dependent DNA polymerase activities as well as RNase H activity that specifically degrades the RNA strand of RNA-DNA duplexes. At some stages of the replication a strand-displacement activity of RT is also necessary. All activities are essential for the conversion of single-stranded genomic RNA into the double-stranded preintegrative DNA. This review focuses on the role of RT in the different steps of the replication process of retroelements. The features of retrotransposon replication which differ from the retroviral ones will be emphasized. In a second part of the review, the biochemical and enzymatic properties of two newly characterized retrotransposon RTs will be described. The role of the integrase domain in reverse transcriptase activity of some retroviral and retrotransposon RTs will be discussed.
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PMID:Reverse transcription of retroviruses and LTR retrotransposons. 1157 82


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