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)

We have detected in rat liver cytosol three enzymes (termed C-1, C-2, and C-3) which cleaved the RNA moiety of RNA-DNA hybrid. These enzymes were separated from each other by DEAE-Sephadex and Sephadex G-200 chromatography. C-1 and C-2 specifically act on the RNA moiety of RNA-DNA hybrid, while C-3 degrades single-stranded RNA as well as the RNA of the hybrid. The molecular weights of C-1, C-2, and C-3 are about 110,000, 35,000 and 110,000 daltons, respectively, and their activities are absolutely dependent on divalent cations such as Mg2+ and Mn2+. Cleavage by C-1 and C-2 is endonucleolytic, producing mostly oligonucleotides and a small amount of mononucleotides which possess 3'-hydroxyl termini. It seems likely that C-2 is originally present in the nucleus and is released into cytosol because of its loose binding to the nuclear components. As for biochemical properties, C-1 is very similar to the cytosol ribonuclease H initially reported by Roewekamp and Sekeris, and C-2 is very similar to the nuclear ribonuclease H reported by us in the preceding paper.
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PMID:Ribonuclease H from rat liver. II. Partial purification and characterization of cytosol ribonuclease H1. 2 90

DNA polymerase was purified to apparent electrophoretic homogeneity from virions of spleen necrosis virus (SNV). (SNV is a member of the reticuloendotheliosis group of avian ribodeoxyviruses). The SNV DNA polymerase appears to consist of a single polypeptide with a molecular weight of 68,000. The SNV DNA polymerase has a preference for Mn2+ for DNA synthesis with an RNA template and Mg2+ for DNA synthesis with a deoxyribohomopolymer template. At the optimum concentrations of divalent cation, the relative rates of DNA synthesis by SNV DNA polymerase with different template.primers were similar to the relative rates of DNA synthesis by an avian leukosis virus DNA polymerase, with the exception of a lower relative rate of DNA synthesis by SNV DNA polymerase with SNV RNA. However, in contrast to DNA synthesized by the avian leukosis virus DNA polymerase with a SNV RNA template, DNA synthesized by SNV DNA polymerase with an SNV RNA template did not hybridize to the SNV RNA. SNV DNA polymerase has RNase H activity which is antigenically distinct from the RNase H activity of avian leukosis-sarcoma virus DNA polymerase.
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PMID:Purification and properties of spleen necrosis virus DNA polymerase. 5 34

Crude extracts of Escherichia coli selectively convert fd viral DNA and not phiX174 DNA to duplex DNA via a complex series of reactions one of which involves RNA polymerase. Reactions leading to formation of fd duplex-replicative (RFII) structures have been reconstituted with purified proteins from E. coli. Maximal synthesis requires the combined action of E. coli binding protein, DNA elongation factor I, DNA elongation factor II preparations (which are a mixture of dna Z and DNA elongation factor III), DNA polymerase III, DNA-dependent RNA polymerase, Mg2+, dATP, dGTP, dCTP, dTTP, and ATP, GTP, CTP, and UTP. In contrast to crude extracts of E. coli, purified protein fractions do not distinguish between fd DNA and phiX174 DNA in duplex DNA formation. The addition of crude fractions of E. coli to the purified components listed above selectively permits fd RFII formation and prevents phiX RFII formation. This selective inhibition was used as an assay to isolate proteins essential for this phenomenon; they include RNase H, discriminatory factor alpha, and discriminatory factor beta.
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PMID:Selective inhibition of in vitro DNA synthesis dependent on phiX174 compared with fd DNA. I. Protein requirements for selective inhibition. 14 Jan 66

A DNA endonuclease, Endo-I, which cleaves superhelical DNAs, has been isolated from avian myeloblastosis virions stripped of their coats by mild detergent treatment. The enzyme has a broad pH optimum around 7.5-8.0 and requires Mg2+ for activity. A second endonuclease, Endo-II, with a requirement for Mn2+, also present in viral cores, copurified with avian myeloblastosis virus alpha beta DNA polymerase (reverse transcriptase, RNA-dependent DNA nucleotidyltransferase) and similarly cleaved superhelical DNAs. Heat denaturation and sodium fluoride and N-ethylmaleimide inhibition studies were carried out to demonstrate a possible relationship between the two endonucleases and the viral DNA polymerase and RNase H activities. It appears that Endo-II may be an intrinsic activity of the polymerase.
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PMID:DNA endonucleases associated with the avian myeloblastosis virus DNA polymerase. 22 53

Two forms of enzyme with ribonuclease H (RNase H) [EC 3.1.4.34] activities, have been partially purified from cultured plant cells, strain GD-2, derived from carrot root. One is an Mn2+-dependent RNase H, and the second is an Mg2+-dependent RNase H. These enzymes degrade RNA specifically in RNA-DNA hybrid structures. They were eluted at around 0.2 M and 0.4 M potassium chloride in phosphocellulose chromatography, and were further purified using blue Sepharose. Mg2+-dependent RNase H exhibits maximal activity at pH 9.0, and requires 10 to 15 mM Mg2+ for maximal activity, whereas the Mn2+-dependent enzyme is most active at pH 8.0, is maximally active at an Mn2+ concentration of 0.4 mM, and has some activity with Mg2+. Both enzymes require a sulfhydryl reagent for maximal activity. The enzymes liberate a mixture of oligonucleotides with 5'-phosphate and 3'-hydroxyl termini. The apparent molecular weight of the Mg2+-dependent RNase H was estimated to 18--20 X 10(4) and that of the Mn 2+- dependent RNase H was estimated to be 14 x 10(4) by gel filtration.
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PMID:Two ribonucleases H from cultured plant cells. 44 17

Three types of ribonuclease H were detected in the isolated macronuclei of Tetrahymena pyriformis GL, partially purified and characterized. They were eluted at around 0.15 M, 0.3 M and 0.4 M of ammonium chloride in phosphocellulose chromatography, and termed H-1, H-2 and H-3, respectively. The partially purified enzymes have following properties. a) These enzymes specifically hydrolyze the RNA moiety of RNA . DNA hybrid. Neither DNA moiety of RNA . DNA hybrid nor the RNA molecule dissociated by heat from RNA . DNA hybrid is hydrolyzed by these enzymes. b) The enzymes are most active at pH 8.5-9.0. c) They require divalent cations such as Mg2+ or Mn2+ for their activities. The optimal concentrations of these cations are different among these enzymes. d) The mode of cleavage by these enzymes is endonucleoytic, producing mostly oligonucleotides and a small amount of mononucleotides which possess 3'-hydroxyl and 5'-phosphate termini.
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PMID:Multiple forms of nuclear ribonuclease H from Tetrahymena pyriformis. 81 68

When the action of highly purified specimens of ribonuclease H (hybrid nuclease; RNA-DNA hybrid ribonucleotidohydrolase; EC 3.1.4.34) of calf thymus on a wide selection of homopolymer hybrids was studied, the extent, and even the occurrence, of hydrolysis was found to be governed by the interplay of several factors: the composition of the ribo strand, the length of the deoxyribo strand, and the nature of the activating metal. Mn2+ activates the enzymic cleavage of all hybrid combinations, Mg2+ only of those containing purine ribo strands, Co2+ only of poly(A) hybrids. A 1:1 hybrid of phage f1 DNA and RNA is, however, split in the presence of any of these activators. Hybrids with deoxyribo tetranucleotides can still be cleaved, but not with dinucleotides. The behavior of hybrids containing covalently linked runs of ribo and deoxyribopolynucleotides was studied with the hybrid poly(dT)-poly(A)7-(dA)X]. This hybrid is attacked by ribonuclease H so that the bulk of the resulting poly(dA) still retains one covalently linked riboadenylic acid end group, whereas a small proportion carries a ribo dinucleotide. Inhibition studies showed that ribonuclease H is inactivated irreversibly by pretreatment with S-adenosylmethionine at 35 degrees, but not at 0 degrees. S-Adenosylhomocysteine also is inhibitory, but not irreversibly; also it is essentially limited to the inhibition of the cleavage of purine ribo strands. When the enzyme is exposed simultaneously to both inhibitors, irreversible inactivation is diminished considerably.
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PMID:Ribonuclease H of calf thymus: substrate specificity, activation, inhibition. 106 91

Reverse transcription of retroviral genomes requires the action of an RNase H for template switching and primer generation. In this report, we compare enzymatic properties of the RNase H associated with the reverse transcriptase (RT) from feline immunodeficiency virus (FIV) and that from human immunodeficiency virus (HIV). Both enzymes displayed substrate preference for poly[3H](rG) . poly(dC) hybird over poly[3H](rA) . poly(dT) and cation preference for Mg2+ over Mn2+. Activity of the FIV RNase H upon poly(rG) . poly(dC) produced hydrolysis products from 1 to 6 nucleotides in length, similar to that reported for HIV. Dextran sulfates were effective inhibitors of both the FIV and HIV RNase H and RT activities. Nearly identical inhibition constants (0.12 nM) were obtained for all enzyme activities with dextran sulfate 500,000, while different inhibition constants were observed with dextran sulfate 8,000. Our results suggest that FIV and HIV RTs contain a conserved region that is sensitive to the larger dextran sulfate and that dextran sulfate 8,000 may interact at a different site or by a different mechanism.
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PMID:RNase H activity associated with reverse transcriptase from feline immunodeficiency virus. 137 May 49

The mobile element jockey is similar in structural organization and coding potential to the LINEs of various organisms. Current models of the mechanism of transposition involve reverse transcription of an RNA intermediate and utilization of element-encoded proteins. As it is demonstrated here, a 2.23 kb DNA fragment from the region of the jockey encoding the putative reverse transcriptase, was stably introduced into the expression system under inducible control of the Escherichia coli lac regulatory elements. We describe the expression of the 92 kDa protein and identify this polypeptide alone as authentic jockey reverse transcriptase based on some of its physical and enzymic properties. The jockey polymerase demonstrates RNA-directed and DNA-directed DNA polymerase activities, but lacks detectable RNase H, has a temperature optimum at 26 degrees C, requires Mg2+ or Mn2+ as a cofactor and is inactivated by sulfhydryl reagent. The enzyme prefers poly(rC) and poly(rA) as template and "activated" DNA is not effective. The results of this work suggest that the RNA-directed DNA polymerase coded by jockey elements may be involved in the transcription of the elements.
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PMID:[Cloning and expression in Escherichia coli of reverse transcriptase coded by the mobile genetic element jockey]. 138 Jun 45

Porcine liver DNA polymerase gamma was shown previously to copurify with an associated 3' to 5' exonuclease activity (Kunkel, T. A., and Mosbaugh, D. W. (1989) Biochemistry 28, 988-995). The 3' to 5' exonuclease has now been characterized, and like the DNA polymerase activity, it has an absolute requirement for a divalent metal cation (Mg2+ or Mn2+), a relatively high NaCl and KCl optimum (150-200 mM), and an alkaline pH optimum between 7 and 10. The exonuclease has a 7.5-fold preference for single-stranded over double-stranded DNA, but it cannot excise 3'-terminal dideoxy-NMP residues from either substrate. Excision of 3'-terminally mismatched nucleotides was preferred approximately 5-fold over matched 3' termini, and the hydrolysis product from both was a deoxyribonucleoside 5'-monophosphate. The kinetics of 3'-terminal excision were measured at a single site on M13mp2 DNA for each of the 16 possible matched and mismatched primer.template combinations. As defined by the substrate specificity constant (Vmax/Km), each of the 12 mismatched substrates was preferred over the four matched substrates (A.T, T.A, C.G, G.C). Furthermore, the exonuclease could efficiently excise internally mismatched nucleotides up to 4 residues from the 3' end. DNA polymerase gamma was not found to possess detectable DNA primase, endonuclease, 5' to 3' exonuclease, RNase, or RNase H activities. The DNA polymerase and exonuclease activities exhibited dissimilar rates of heat inactivation and sensitivity to N-ethylmaleimide. After nondenaturing activity gel electrophoresis, the DNA polymerase and 3' to 5' exonuclease activities were partially resolved and detected in situ as separate species. A similar analysis on a denaturing activity gel identified catalytic polypeptides with molecular weights of 127,000, 60,000, and 32,000 which possessed only DNA polymerase gamma activity. Collectively, these results suggest that the polymerase and exonuclease activities reside in separate polypeptides, which could be derived from separate gene products or from proteolysis of a single gene product.
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PMID:Properties of the 3' to 5' exonuclease associated with porcine liver DNA polymerase gamma. Substrate specificity, product analysis, inhibition, and kinetics of terminal excision. 166 14


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