UMLS:C0023418 - FACTA Search

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Query: UMLS:C0023418 (leukemia)
93,477 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two RNase H (RNA-DNA hybrid ribonucleotidohydrolase, EC 3.1.4.34) activities separable by Sephadex G-100 gel filtration were identified in lysates of Moloney murine sarcoma-leukemia virus (MSV). The larger enzyme, which we have called RNase H-I, represented about 10% of the RNase H activity in the virion. RNase H-I (i) copurified with RNA-directed DNA polymerase from the virus, (ii) had a sedimentation coefficient of 4.4S (corresponds to an apparent mol wt of 70,000), (iii) required Mn-2+ (2 mM optimum) for activity with a [3-h]poly(A)-poly(dT) substrate, (iv) eluted from phosphocellulose at 0.2 M KC1, and (v) degraded [3-H]poly(A)-poly(dT) and [3-H]poly(C)-poly(dG) at approximately equal rates. The smaller enzyme, designated RNase H-II, which represented the majority of the RNase H activity in the virus preparation, was shown to be different since it (i) had no detectable, associated DNA polymerase activity, (ii) had a sedmimentation coefficient of 2.6S (corresponds to an apparent mol wt of 30,000), (iii) preferred Mg-2+ (10 to 15 mM optimum) over Mn-2+ (5 to 10 mM optimum) 2.5-fold for the degradation of [3-H]poly(A)-poly(dT), and (iv) degraded [3-H]poly(A)-poly(dT) 6 and 60 times faster than [3-H]poly(C)-poly(dG) in the presence of Mn-2+ and Mg-2+, respectively. Moloney MSV DNA polymerase (RNase H-I), purified by Sephadex G-100 gel filtration followed by phosphocellulose, poly(A)-oligo(dT)-cellulose, and DEAE-cellulose chromatography, transcribed heteropolymeric regions of avian myeloblastosis virus 70S RNA at a rate comparable to avian myeloblastosis virus DNA polymerase purified by the same procedure.
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PMID:Purification and characterization of the DNA polymerase and RNase H activities in Moloney murine sarcoma-leukemia virus. 4 24

DNA polymerase was purified from a cloned isolate of Moloney murine leukemia virus (M-MuLV). Purified M-MuLV DNA polymerase, upon analysis by polyacrylamide gel electrophoresis, showed one major polypeptide of mol wt 80,000. Estimation of molecular weight from the sedimentation rate of the purifed enzyme in a glycerol gradient was consistent with a structure containing one polypeptide. M-MuLV DNA polymerase could transcribe ribopolymers, deoxyribopolymers, and heteropolymers as efficiently as did purified DNA polymerase from avian myeloblastosis virus (AMV). M-MuLV DNA polymerase, however, transcribed native 70S viral RNA less efficiently than did AMV DNA polymerase. Addition of oligo(dT) enhanced five to tenfold the transcription of 70S viral RNA by M-MuLV DNA polymerase. Purified enzyme also exhibited nuclease activity (RNase H) that selectively degraded the RNA moiety of the RNA-DNA hybrid. It did not degrade single-stranded RNA, single-stranded DNA, double-stranded RNA, and double-stranded DNA. M-MuLV DNA polymerase-associated RNase H acted as a random exonuclease. When [3-H]poly(A)-poly(dT) was used as a substrate, the size of the M-MuLV DNA polymerase-associated RHase H digested product was larger than the size of the digestion products by AMV DNA polymerase. The oligonucleotide digestion products could be further digested to 5'-AMP by snake venom phosphodiesterase, indicating that the products were terminated by 3'-OH groups. Alkaline hydrolysis of the oligonucleotide digestion products generated pAp, suggesting that M-MuLV DNA polymerase-associated RNase H cleaves at the 3' side of the 3',5'-phosphodiester bond. The ratios of the rates of DNA polymerase activity and RNase H activity were not significantly different in the murine and avian enzymes.
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PMID:Studies on reverse transcriptase of RNA tumor viruses III. Properties of purified Moloney murine leukemia virus DNA polymerase and associated RNase H. 4 25

We have investigated three aspects of RNA turmor virus replication and cell transformation: (1) the properties of the purified avian and mammalian viral RNA-directed DNA polumerase, (2) some characteristics of the viral 60-70S RNA genome, 30-40S RNA subunits and intracellular viral RNA species, and (3) the interaction of the viral DNA polymerase with its RNA template early during infection and cell transformation by the murine sarcoma-leukemia virus (MSV[MLV]). Avian myeloblastosis virus (AMV) contains two forms of RNA-directed DNA polymerase, alpha, consisting of a single polypeptide of molecular weight 65,000, and alphabeta, consisting of two polypeptides of molecular weights 65,000 and 105,000. The alpha and alphabeta forms of AMV DNA polymerase both possess RNase H activity that requires free end termini on the ribopolymer and can degrade the RNA of the RNA-DNA hybrid in the 3' to 5' and 5' to 3' directions. But, alpha and alphabeta possess a different mode of exoribonuclease activity. While alphabeta RNase H is a processive exoribonuclease that degrades the polynucleotide chain to a core residue before attacking a second chain, alpha RNase H is a random exoribonuclease that releases the polynucleotide after each scission. Highly purified Moloney-MSV(MLV) DNA polymerase has both RNase H activity and the ability to read viral 60-70S RNA. These activities comigrate through five different steps of purification and are present at levels comparable to those found in purified AMV DNA polymerase. The MSV(MLV) 60-70S RNA genome and 35S RNA subunits were shown by periodate oxidationtritiated borohydride reduction to contain adenosine as the major 3'-terminal nucleoside. Poly (A) segments were isolated from viral 60-70S and 35S RNA by treatment with RNase A or RNase T1 and purified by afinity chromatography and gel electrophoresis. Viral poly(A) was shown to be present at the 3' terminus as -G(C,U)A190AOH. The similar sequence reported for poly(A) present in mammalian mRNA suggests that similar mechanisma are involved in the transcription and processing of both cellular and viral DNA sequences. Within transformed cells replicating MSV(MLV), viral 35S and 20S RNA were found in membrane-bound polyribosomes, whereas only 35S RNA was detected in free polyribosomes. The origin and function of 20S RNA is unknown. The early events during rapid infection and cell transformation of mouse 3T6 cells by the Harvey strain of MSV(MLV) were studied. By both autoradiographic analysis and molecular hybridization, viral DNA synthesis was detected in the cytoplasm by 1 hour after infection, reached a maximum at 2 hours, and subsequently decreased. Cytological chase experiments produced evidence that cytoplasmic viral DNA was transported to the nucleus. In situ hybridization experiments using radioactive viral DNA product as a probe demonstrated the rapid association of viral DNA sequences with the chromocenters of interphase nuclei and with the centromeric heterochromatin regions of some chromosomes.
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PMID:Properties of oncornavirus RNA-directed DNA polymerase, the RNA template, and the intracellular products formed early during infection and cell transformation. 5 Sep 2

The alpha beta DNA polymerase of avian myeloblastosis virus was treated with dimethyl sulfoxide to dissociate the enzyme subunits. The dimethyl sulfoxide treated enzymes were passed over phosphocellulose to purify and characterize the dissociated subunits as well as to remove the dimethyl sulfoxide. RNA-directed DNA polymerase, RNase H, and nucleic acid-binding activity were monitored, as well as the subunit structure (on sodium dodecyl sulfate-polyacrylamide gels) of the various enzyme species obtained. With 30% dimethyl sulfoxide, the majority of DNA polymerase and RNase H activities as well as the alpha subunit were displaced from the alpha beta DNA polymerase position on phosphocellulose (0.23 M potassium phosphate) to the alpha DNA polymerase position (0.1 M). The association of DNA polymerase and RNase H activities with the alpha subunit suggests that alpha is the enzymatically active subunit in alpha beta. In addition to alpha DNA polymerase, a minor polymerase species eluted from phosphocellulose at 0.4 M potassium phosphate. The dissociated beta subunit eluted from phosphocellulose at a wide range of salt concentrations (0.28 to 0.5 M potassium phosphate). The dissociated beta subunit bound 3H-labeled murine leukemia virus RNA and [3H]poly(dT)-poly(dA) approximately 20-fold more avidly than alpha DNA polymerase alone. In contrast to the results with the alpha subunit, there was no correlation between DNA polymerase and RNase H activity profiles and the elution profile of the beta subunit from phosphocellulose. These observations suggest the beta subunit is either enzymatically inactive or possesses limited DNA polymerase and RNase H activity when compared with the alpha subunit.
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PMID:Dissociation of alpha beta DNA polymerase of avian myeloblastosis virus by dimethyl sulfoxide. 5 61

The purified reverse transcriptase-RNase H complex from Friend murine leukemia virus consists of a single polypeptide of 84,000 molecular weight, which after mild protease treatment in vitro or after intentional degradation during the purification procedure allows the generation of several additional polypeptides. Degradation destroys the RNA-dependent DNA polymerase activity with native RNA templates and reduces RNase H but does not affect response to synthetic template primers such as poly (rA)-Oligo (dT). The properties of the intact murine enzyme consisting of a single polypeptide of 84,000 molecular weight are compared to those of the avian alpha subunit and the avian alpha beta enzyme complex. The intact murine enzyme resembles the avian beta-containing enzyme complex and is different from alpha in the following respects: (i) it binds to native RNA templates; (ii) it transcribes native RNA templates into DNA, a reaction which can be inhibited by actinomycin D; (iii) RNase H activity behaves like a processive exonuclease; and (iv) analysis of the RNase H digestion products reveals oligonucleotides approximately four bases in length.
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PMID:Further characterization of the Friend murine leukemia virus reverse transcriptase-RNase H complex. 5 72

Rauscher leukemia virus RNA-directed DNA polymerase has been purified to near homogeneity (greater than 90% pure) using affinity chromatography on polycytidylate-agarose with over 85% recovery of input enzymatic activity. The purified enzyme has a molecular weight of approximately 70,000 and appears to consist of a single polypeptide chain. The enzyme is free of DNase, but has RNase H activity. Analysis of the requirements for optimal rates of DNA synthesis by this enzyme using synthetic and natural template-primers has revealed template-specific variations in such requirements. During these studies it was observed that DNA synthesis catalyzed by Rauscher leukemia virus DNA polymerase is inhibited by the addition of inorganic phosphate. An analysis of the mechanism of phosphate inhibition was carried out using the synthetic template-primer poly(A)-(dT)10. It appears that by some mechanism, possibly involving the substrate binding site of the enzyme, phosphate ions inhibit DNA synthesis with a more acute effect on the rate of chain growth than on that of initiation. The extension of these studies to DNA synthesis catalyzed by a variety of mammalian type C viral reverse transcriptases revealed that low levels ( less than or equal to 2 mM) of inorganic phosphate strongly inhibited DNA synthesis. The susceptibility to phosphate inhibition appears unique to mammalian type C viral enzymes since the type B viral enzyme, Escherichia coli DNA polymerase I, avian myeloblastosis virus and Mason Pfizer monkey tumor virus reverse transcriptase and cellular DNA polymerases alpha and gamma are not inhibited by inorganic phosphate. This phenomenon of phosphate inhibition of various DNA polymerases, therefore, provides a new basis for the differentiation of the sources and nature of these enzymes.
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PMID:Purification and properties of Rauscher leukemia virus DNA polymerase and selective inhibition of mammalian viral reverse transcriptase by inorganic phosphate. 6 68

The RNase H activity associated with several RNA-directed DNA polymerases is inhibited by the addition of DNA, in contrast to RNase H activity from enzymes devoid of polymerizing activity. Kinetic investigations of the inhibitory effect of DNA, using purified Rauscher leukemia virus DNA polymerase as a test enzyme, revealed that the addition of DNA to an ongoing RNase H reaction causes an immediate cessation of RNase H activity. Concomitant initiation of DNA synthesis by inhibitory DNA can occur, provided that appropriate substrate and primer is available. Thus, in addition to providing a simple test for the distinction between polymerase-associated and polymerase-independent RNase H activity, this study strongly supports the concepts that (i) RNase H activity expressed by several mammalian oncoviral reverse transcriptases is an integral part of that molecule, and (ii) that the catalytic site of RNase H activity is also involuved in template-primer binding.
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PMID:Specific inhibition of DNA polymerase-associated RNase H by DNA. 6 22

Lysates of Moloney murine sarcoma-leukemia virus [M-MSV(MLV)], a virus complex grown in the rat cell line 78A-1, were found to contain three RNase H species separable by polycytidylic acid[poly(C)]-agarose chromatography. RNase H activity (RNase H I) associated with RNA-directed DNA polymerase eluted at 0.23 M KCI from poly(C)-agarose. RNase H II, which eluted from poly(C)-agarose at 0.12 M KCI and was not associated with DNA polymerase activity, was shown to be identical to an RNase H species (designated RNase H II) previously isolated from M-MSV(MLV) by a different procedure (G. F. Gerard and D. P. Grandgenett, J. Virol. 15:785-797, 1975). M-MSV(MLV) RNase H II was established to be a random exohybridase that requires free-chain termini in its hybrid substrate for activity. Lysates of Rickard feline leukemia virus also contained RNase H activity not associated with DNA polymerase activity that eluted from poly(C)-agarose at 0.12 M KCl. A third species of enzyme from M-MSV(MLV) lysates, called RNase H III, did not bind to poly(C)-agarose in 0.06 M KCl. RNase H III was purified from lysates of M-MSV(MLV) and M-MLV (grown in mouse cells) by sequential chromatography on poly(C)-agarose, DEAE-cellulose, phosphocellulose, and polyuridylic acid-Sepharose. Purified RNase H III (i) was free of any associated DNA polymerase activity, (ii) had an apparent molecular weight of 30,000 determined by Sephadex G-100 gel filtration, (iii) had an absolute requirement for Mn2+ (1 mM optimum) for the degradation of [3H](A)n.(dT)n, (iv) was inhibited by the presence of any salt in reaction mixtures, and (v) was endoribonucleolytic in its mode of action as indicated by the size distribution of limited degradation products of [3H](A)n.(dT)n. RNase H III was inhibited by antisera prepared against Rauscher MLV and simian sarcoma virus reverse transcriptase, and the quantity of RNase H III and RNase H I present in lysates of M-MLV were reduced and increased proportionately if virus was lysed in the presence of the protease inhibitor phenylmethylsulfonyl fluoride. These results indicate that RNase H III is a proteolytic cleavage product of DNA polymerase-RNase H. Substantial RNase H activity that did not bind to poly(C)-agarose in 0.06 M KCl was also found in lysates of Harvey MSV(MLV), Rauscher MLV, and Rickard feline leukemia virus, but not in lysates of avian myeloblastosis virus.
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PMID:Multiple RNase H activities in mammalian type C retravirus lysates. 7 33

We reported earlier that core preparations of Rauscher murine leukemia virus, when separated on an isopycnic sucrose gradient, did not contain detectable levels of RNase H activity, while retaining high levels of reverse transcriptase activity. We reexamined this phenomenon, and the earlier observation was found to be reproducible. However, when doubly banded preparations of viral cores were solubilized and reverse transcriptase was isolated by ion-exchange chromatography, a coincident peak of a nuclease activity with the specificity of RNase H was observed, which indicated that RNase H was selectively inhibited in the core fractions. By direct activity measurements using the purified reverse transcriptase-RNase H from cores, this endogenous inhibitor has been identified as the viral RNA. Viral 70S RNA strongly inhibited RNase H activity purified either from whole virions or from prefractionated cores. Other RNAs tested that had inhibitory effects were yeast tRNA, polyadenylic acid, and polyguanylic acid. Polyuridylic acid and polyadenylic acid were moderately inhibitory, and polycytidylic acid did not inhibit the RNase H. A rabbit anti-reverse transcriptase immunoglobulin G inhibited both the reverse transcriptase and RNase H activities of the enzyme purified from cores. These data provide a rational explanation for the failure to detect RNase H activity in core preparations of Rauscher murine leukemia virus. Furthermore, these data are consistent with the idea that the RNase H and reverse transcriptase activities purified from cores reside on the same protein molecule. Possible biological implications of the observed inhibition of RNase H by RNA is discussed.
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PMID:Inhibition by RNA of RNase H activity associated with reverse transcriptase in Rauscher murine leukemia virus cores. 8 12

The RNase H activity associated with purified avian myeloblastosis virus and Rauscher murine leukemia virus DNA polymerases is inhibited by homopolymeric RNA molecules, although the efficiency of inhibition by each homopolymer appears enzyme specific. Formation of duplex RNA molecules abolished the inhibitory activity. In contrast to these results, DNA polymerase-independent RNase H activities, such as the RNase H-II from Rauscher murine leukemia virus and calf thymus RNase H, were unaffected by the addition of exogenous RNA molecules to reaction mixtures. These results support the concept (M. J. Modak and S. L. Marcus, J. Virol. 22:253--256, 1977) that the catalytic site of DNA polymerase-associated RNase H activity may be that which is also involved in template binding. Naturally occurring RNA molecules of oncornaviral, procaryotic, or eucaryotic origin also proved to be efficient inhibitors of avian myeloblastosis virus DNA polymerase-associated RNase H activity. In contrast to this result, naturally occurring RNA molecules, at concentrations which inhibited the avian myeloblastosis virus enzyme, did not inhibit Rauscher murine leukemia virus DNA polymerase-catalyzed RNase H activity. This finding represents a new biochemical distinction between the two reverse transcriptases, and may be indicative of differences in the relative affinities of these enzymes for natural RNA molecules.
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PMID:Reverse transcriptase-associated RNase H activity. II. Inhibition by natural and synthetic RNA. 8 13

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