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)

An RNase H was purified 2,500-fold to near homogeneity from early embryos of Drosophila melanogaster. The purified enzyme has an approximate molecular weight of 180,000 and appears to consist of two 49,000- and two 39,000-dalton polypeptides. The enzyme specifically hydrolyzes RNA.DNA hybrids and releases oligoribonucleotides ranging in size from 2-9 residues. The RNase H can also remove RNA primers that are synthesized and subsequently elongated by the Drosophila polymerase-primase. Preincubation of the RNase H from D. melanogaster embryos with the homologous DNA polymerase-primase results in an increased rate of DNA synthesis. The DNA chains synthesized under these conditions are shorter than those synthesized in the absence of the RNase H, and the rate of primer synthesis is increased significantly. These findings suggest that the RNase H forms a complex with the polymerase-primase, increasing its recycling capacity and thereby increasing the frequency of chain initiation.
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PMID:Interaction of ribonuclease H from Drosophila melanogaster embryos with DNA polymerase-primase. 299 23

The mutD(dnaQ) gene in Escherichia coli codes for the epsilon subunit of the DNA polymerase pol III holoenzyme. Previous work has shown that this gene lies adjacent to the gene coding for RNase H (rnh). The two products are translated from diverging promoters. Here we report on the 1.6 kb (1 kb = 10(3) bases or base-pairs) sequence of the region coding for both genes, and the transcripts encoded by them. mutD codes for two transcripts, one of whose origins lies within the rnh structural gene. Both transcripts overlap and are complementary to a region of the rnh transcript. Thus, they can potentially form double-stranded helices with rnh. Of the two possible double-stranded structures, the shorter does not interfere with a likely rnh ribosome binding site, while the longer one does. We suggest that this unique organization may regulate rnh translation rates.
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PMID:DNA sequence and coding properties of mutD(dnaQ) a dominant Escherichia coli mutator gene. 302 34

Infectious hamster leukemia virus (HaLV) contains a DNA polymerase different from those of murine and avian viruses. No endogenous reaction directed by the 60 to 70S RNA of HaLV could be demonstrated in detergenttreated HaLV virions, nor could the purified DNA polymerase copy added viral RNA. The virion RNA could, however, act as template for added avian myeloblastosis virus DNA polymerase and the HaLV DNA polymerase could efficiently utilize homopolymers as templates. The HaLV enzyme was like other reverse transcriptases in that certain ribohomopolymers were much better templates than the homologous deoxyribohomopolymers. No ribonuclease H activity could be shown in the HaLV enzyme, but neither could activity be found in the murine leukemia virus DNA polymerase. The hamster enzyme was unique in that poly(A) .oligo(dT) was a poor template, and globin mRNA primed with oligo(dT) was totally inactive as a template. Its uniqueness was also indicated by its subunit composition; electrophoresis of the HaLV DNA polymerase in sodium dodecyl sulfate-containing polyacrylamide gels revealed equimolar amounts of two polypeptides of molecular weight 68,000 and 53,000. The sedimentation rate of the enzyme in glycerol gradients was consistent with a structure containing one each of the two polypeptides. The enzyme thus appears to be structurally distinct from other known virion DNA polymerases. Its inability to carry out an endogenous reaction in vitro might result from an inability to utilize certain primers.
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PMID:Hamster leukemia virus: lack of endogenous DNA synthesis and unique structure of its DNA polymerase. 413 18

Ribonuclease H (RNA.DNA-hybrid ribonucleotidohydrolase, EC 3.1.4.34) has been reported to copurify with reverse transcriptase (RNA directed DNA polymerase) of RNA tumor viruses. In addition, viral specific ribonuclease H and reverse transcriptase of avian type-C viruses are thought to be part of the same polypeptide. In this report we show that a fraction of the ribonuclease H activity from Rauscher murine leukemia and Kirsten murine sarcoma viruses was separated from reverse transcriptase by anion exchange chromatography while the remaining portion co-purified with the viral polymerase. The amount of this co-purified nuclease activity was about 4- to 8-fold lower than the activity found in avian myeloblastosis virus (with respect to the ratio of ribonuclease H to reverse transcriptase) and this nuclease activity can only be detected by using labeled substrate of high specific radioactivity. However, a complete separation of ribonuclease H activity from reverse transcriptase was obtained by purifying core structures of the virus by sucrose density gradient centrifugation. While reverse transcriptase was present in the cores, there was no detectable ribonuclease H. Furthermore, a specific antibody against Rauscher leukemia virus reverse transcriptase did not inhibit any virion associated ribonuclease H activity. Our results suggest that in these virions these two enzyme activities reside in two separate molecules and probably in two different compartments of the virus. These findings emphasize a basic difference between the avian and murine type-C virus DNA polymerases.
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PMID:Separation of ribonuclease H and RNA directed DNA polymerase (reverse transcriptase) of murine type-C RNA tumor viruses. 413 16

Ribonuclease H from human KB cells, chick embryos, calf thymus, avian myeloblastosis virus, and Rous associated virus specifically degrades the RNA of DNA.RNA hybrids, producing mono- and oligoribonucleotides terminated in 5'-phosphates. The cellular RNase H is an endonuclease, whereas the viral enzyme appears to be an exonuclease. Viral DNA polymerase and RNase H copurify through all separation steps. Therefore, RNase H activity is an intrinsic part of the viral DNA polymerase. DNA.RNA hybrids are also degraded by nucleases associated with cellular DNA polymerases and by exonuclease III. However, these nucleases differ from RNase H in their ability to degrade both strands of DNA.RNA hybrids.
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PMID:Degradation of DNA RNA hybrids by ribonuclease H and DNA polymerases of cellular and viral origin. 434 66

Kirsten murine sarcoma-leukemia virus (Ki-MSV[MLV]) was found to contain less RNase H per unit of viral DNA polymerase than avian Rous sarcoma virus (RSV). Upon purification by chromatography on Sephadex G-200 and subsequent glycerol gradient sedimentation the avian DNA polymerase was obtained in association with a constant amount of RNase H. By contrast, equally purified DNA polymerase of Ki-MSV(MLV) and Moloney [Mo-MSV(MLV)] lacked detectable RNase H if assayed with two homopolymer and phage fd DNA-RNA hybrids as substrates. On the basis of picomoles of nucleotides turned over, the ratio of RNase H to purified avian DNA polymerase was 1:20 and that of RNase H to purified murine DNA polymerase ranged between <1:2,800 and 5,000. Based on the same activity with poly (A).oligo(dT) the activity of the murine DNA polymerase was 6 to 60 times lower than that of the avian enzyme with denatured salmon DNA template or with avian or murine viral RNA templates assayed under various conditions (native, heat-dissociated, with or without oligo(dT) and oligo(dC) and at different template enzyme ratios). The template activities of Ki-MSV(MLV) RNA and RSV RNA were enhanced uniformly by oligo(dT) but oligo(dC) was much less efficient in enhancing the activity of MSV(MLV) RNA than that of RSV RNA. It was concluded that the purified DNA polymerase of Ki-MSV(MLV) differs from that of Rous sarcoma virus in its lack of detectable RNase H and in its low capacity to transcribe viral RNA and denatured salmon DNA. Some aspects of these results are discussed.
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PMID:DNA polymerase of murine sarcoma-leukemia virus: lack of detectable RNase H and low activity with viral RNA and natural DNA templates. 435 18

Differential inhibition conditions were established for the DNA polymerase and RNase H activities of avian myeloblastosis virus (AMV) with ether-disrupted AMV and a purified enzyme preparation. The RNase H activity of ether-disrupted AMV with (rA)(n).(dT)(n) and (rA)(n).(dT)(11) as substrates was inhibited 80 to 100% by preincubation with NaF at a final reaction concentration of 27 to 30 mM. Under these conditions, the DNA polymerase activity was inhibited only 0 to 20%. Similar inhibitions were found with exogenous Rous sarcoma virus 35S and 70S RNA.DNA hybrid and phiX174 DNA.RNA hybrid as substrates. Studies were also performed with a purified enzyme preparation, in which the two activities essentially co-purified. The RNase H activity was inhibited >80% by 150 mM KCl with three different hybrid substrates, whereas the DNA polymerase activity was uninhibited. The DNA polymerase was completely inactivated by heat denaturation at 41 C or by omission of the deoxytriphosphates from the reaction mixture; the RNase H remained active. These differential inhibition conditions were used to compare the size of the DNA product synthesized with and without simultaneous RNase H action and to examine the effect of inhibition of the DNA polymerase on the size of the RNase H products. The size of the products of one activity was not affected by inhibition of the other activity. These results suggest that the AMV DNA polymerase and RNase H are not coupled mechanistically.
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PMID:Mechanistic independence of avian myeloblastosis virus DNA polymerase and ribonuclease H. 437 8

R-DNA polymerase, D-DNA polymerase, DNase and RNase H activities in mitochondria from chick embryonic brain were studied by ion-exchange chromatography. Two main fractions were separated according to their chromatographic behaviour: a fraction M Ib which is eluted with the washing buffer from two successive DEAE-cellulose columns and a fraction M IV which is eluted at 400 mM KC1 from a phosphocellulose column. Although the two fractions contain both the DNA polymerase and the degrading activities, all the specific activities are higher in fraction M IV than in fraction M Ib. Heat inactivation experiments have shown that R-DNA polymerase is inactivated in both fractions, whereas RNase H and DNase are not affected. Thus, degrading activities and R-DNA polymerase activity seem to be catalyzed by different molecular entities. However the fact that in most cases these activities co-chromatograph suggests that the corresponding molecules form rather stable complexes.
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PMID:Mitochondrial DNA polymerase, deoxyribonuclease and ribonuclease H activities from brain of chick embryo. 447 11

Progress of the replication forks of the Escherichia coli chromosome depends on a multisubunit DNA polymerase (for chain elongation) and a primosome (for chain initiations), together comprising about 30 polypeptides with a mass in excess of 10(6) daltons. Integration of their actions with those of helicases and DNA binding proteins suggest a more complex and integrated replisome assembly with novel possibilities for concurrent replication of both parental strands. Initiation of a new cycle of chromosome replication at its unique 245-bp (oriC) is being studied in a soluble enzyme system with plasmids, autonomous replication of which depends on the oriC sequence. Required proteins include RNA polymerase, DNA gyrase, dnaA protein (with 4 strong binding sites in oriC), HU protein, and additional proteins (e.g., topoisomerase I and ribonuclease H) that confer oriC specificity by suppressing initiation of replication elsewhere on the duplex DNA. Clarification of the biochemical mechanisms of replication is fundamental for understanding cell growth and development. Knowledge of the biochemistry of initiating a cycle of chromosome replication opens the way toward exploring the regulation of the cell cycle. I remain faithful to the conviction that anything a cell can do, a biochemist should be able to do. He should do it even better, being freed from the constraints of substrate and enzyme concentrations, pH, ionic strength, and temperature, and by having the license to introduce novel reagents to drive or restrain a reaction. Put another way, one can be creative more easily with a reconstituted system. One can grapple directly with the molecules instead of trying by remote means to manipulate their structures or levels in the intact cell. Enzyme purification carries many dangers beyond the well-known exposure of the fragile enzyme to the hostilities of an unfamiliar environment, high dilution, glass containers and a denaturable investigator. But the rewards of enzyme purification have justified the effort. The polymerases, nucleases, ligases purified out of curiosity about the mechanisms of replication, repair and recombination have supplied the cast of actors responsible for the current drama of genetic engineering. Beyond the uses of these enzymes as reagents, understanding the mechanisms of DNA metabolism will have practical value in manipulating the replication of plasmids and viruses and the expression of their genes and, beyond that, in obtaining a more secure grasp of chromosome structure and function.
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PMID:Enzyme studies of replication of the Escherichia coli chromosome. 609 56

Partial chymotryptic digestion of purified avian myeloblastosis virus alpha beta DNA polymerase resulted in the activation of a Mg2+-dependent DNA endonuclease activity. Incubation of the polymerase-protease mixture in the presence of super-coiled DNA and Mg2+ permitted detection of the cleaved polymerase fragment possessing DNA nicking activity. Protease digestion conditions were established permitting selective cleavage of beta to alpha, which contained DNA polymerase and RNase H activity and to a family of polypeptides ranging in size from 30,000 to 34,000 daltons. These latter beta-unique fragments were purified by polyuridylate-Sepharose 4B chromatography and were shown to contain both DNA binding and DNA endonuclease activities. We have demonstrated that this group of polymerase fragments derived by chymotryptic digestion of alpha beta DNA polymerase is similar to the in vivo-isolated avian myeloblastosis virus p32pol in size, sequence, and DNA endonuclease activity.
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PMID:Activation of an Mg2+-dependent DNA endonuclease of avian myeloblastosis virus alpha beta DNA polymerase by in vitro proteolytic cleavage. 615 49


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