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Biomedical subjects

W Levinson

Publications and source records attributed to W Levinson.

At least 109 records · Page 6Linked to original sources
PubMed1973

Inhibition of RNA-dependent DNA polymerase of Rous sarcoma virus by thiosemicarbazones and several cations.

The RNA-dependent DNA polymerase of Rous sarcoma virus is inhibited by N-methyl isatin beta-thiosemicarbazone and by thiosemicarbazide, but not by semicarbazide. These inhibitors also inactivate, upon contact with the virion, the transforming ability of Rous sarcoma virus. Sulfhydryl donors, such as 2-mercapto-ethanol, can prevent these effects. The RNA-directed activity of the purified polymerase is inhibited to a greater degree than is the DNA-directed activity. Two cations, Cu(++) and Hg(++), can inhibit RNA-dependent DNA polymerase and inactivate the transforming ability of the virus. Synergism between N-methyl isatin beta-thiosemicarbazone and Cu(++) occurs, since treatment of the virus with a low dose of either N-methyl isatin beta-thiosemicarbazone or Cu(++) has little effect; however, when the two compounds are mixed together, significant inactivation occurs. This observation supports the hypothesis that the antiviral action of thiosemicarbazones is a function of their ability to act as a ligand for metallic ions. Several cations (Ag(+), Co(++), Zn(++), Cd(++), and Ni(++)) significantly inactivate the RNA-dependent DNA polymerase, but have little effect on the transforming ability. In view of this result, the conclusion that the enzyme activity is required for transformation remains open to question.

Animals↗
PubMed1972

Detection of avian tumor virus-specific nucleotide sequences in avian cell DNAs (reassociation kinetics-RNA tumor viruses-gas antigen-Rous sarcoma virus, chick cells).

The effect of unlabeled cellular DNA upon the reassociation kinetics of labeled double-stranded DNA made by DNA polymerase from avian tumor viruses has been used to measure virus-specific nucleotide sequences in cells. Multiple copies of these sequences were found equally in normal chick cells, in chick cells transformed in culture, and in Rous tumor cells. Copies were also present equally in cells harboring chick helper factor and group-specific antigen, and in cells lacking those characteristics. Quail DNA also contains multiple copies of these sequences, but no copies were detected in HeLa-cell DNA or salmon-sperm DNA.

Animals↗
PubMed1972

Virus-specific ribonucleic acid in cells producing rous sarcoma virus: detection and characterization.

Cells producing Rous sarcoma virus contain virus-specific ribonucleic acid (RNA) which can be identified by hybridization to single-stranded deoxyribonucleic acid (DNA) synthesized with RNA-directed DNA polymerase. Hybridization was detected by either fractionation on hydroxyapatite or hydrolysis with single strand-specific nucleases. Similar results were obtained with both procedures. The hybrids formed between enzymatically synthesized DNA and viral RNA have a high order of thermal stability, with only minor evidence of mismatched nucleotide sequences. Virus-specific RNA is present in both nuclei and cytoplasm of infected cells. This RNA is remarkably heterogeneous in size, including molecules which are probably restricted to the nucleus and which sediment in their native state more rapidly than the viral genome. The nature of the RNA found in cytoplasmic fractions varies from preparation to preparation, but heterogeneous RNA (ca. 4-50S), smaller than the viral genome, is always present in substantial amounts.

Aspergillus↗
PubMed1971

Deoxyribonucleic acid polymerase associated with avian tumor viruses: secondary structure of the deoxyribonucleic acid product.

The products of the deoxyribonucleic acid (DNA) polymerase associated with Rous sarcoma virus and avian myeloblastosis virus were characterized by correlative analyses with equilibrium centrifugation and stepwise elution from hydroxyapatite. The initial enzymatic product consists of nascent DNA chains which are hydrogen-bonded to 70S viral ribonucleic acid (RNA), whereas the final enzymatic product is double-stranded DNA. Appreciable amounts of free single-stranded DNA were not detected at any point during the course of the enzymatic reaction, but the data in this regard are not decisive. The time course of synthesis of DNA:RNA hybrids and double-stranded DNA has been analyzed. It is concluded that the synthesis of double-stranded DNA is a sequel to and is probably dependent upon the synthesis of DNA:RNA hybrid.

Animals↗
PubMed1971

Deoxyribonucleic acid polymerases of Rous sarcoma virus: kinetics of deoxyribonucleic acid synthesis and specificity of the products.

The deoxyribonucleic acid (DNA) polymerase(s) of Rous sarcoma virus synthesizes two principal products-single-stranded DNA in the form of a DNA:ribonucleic acid (RNA) hybrid and double-stranded DNA. All of the single-stranded product and 50% of the double-stranded product can be hybridized to 70S viral RNA. These results, in combination with data obtained by analysis of the kinetics of double-stranded DNA synthesis, indicate that the synthesis of double-stranded DNA is a sequel to the synthesis of single-stranded DNA and is dependent upon the latter for the provision of initial template.

Animals↗
PubMed1971

Deoxyribonucleic acid polymerase of Rous sarcoma virus: studies on the mechanism of double-stranded deoxyribonucleic acid synthesis.

The deoxyribonucleic acid (DNA) polymerase of Rous sarcoma virus synthesizes both single- and double-stranded DNA, utilizing the ribonucleic acid (RNA) of the viral genome as the initial template. Results of pulse-chase experiments indicate that the single-stranded DNA serves as unconserved template and precursor for the synthesis of double-stranded DNA. The latter reaction is apparently initiated in association with the viral RNA and may involve a partially double-stranded intermediate form.

Animals↗
PubMed1971

Deoxyribonucleic acid polymerase(s) of Rous sarcoma virus: effects of virion-associated endonuclease on the enzymatic product.

Purified preparations of Rous sarcoma virus (RSV) contain ribonuclease which is either a constituent of the virion surface or an adsorbed contaminant. Treatment of the virus with nonionic detergent to activate ribonucleic acid (RNA)-dependent deoxyribonucleic acid (DNA) polymerase renders the viral genome susceptible to hydrolysis by the external ribonuclease. The extent of this susceptibility can be substantially reduced by the use of limited amounts of detergent. At a concentration of detergent which provides a maximum initial rate of DNA synthesis, the degradation of endogenous viral RNA results in a reduced yield of high molecular weight DNA: RNA hybrid from the polymerase reaction. Attempts to detect virion-associated deoxyribonuclease, by using a variety of double helical DNA species as substrates, have been unsuccessful, but small amounts of nuclease activity directed against single-stranded DNA may be present in purified virus.

Avian Sarcoma Viruses↗
PubMed1970

Deoxyribonucleic acid polymerase associated with Rous sarcoma virus and avian myeloblastosis virus: properties of the enzyme and its product.

Deoxyribonucleic acid (DNA) polymerase activity can be elicited in purified preparations of avian myeloblastosis virus and Rous sarcoma virus (Schmidt-Ruppin strain) by treatment with nonionic detergent. The enzyme(s) and its synthetic products appear to be virion-associated. Enzymatic activity can be inhibited by pretreatment with either ribonuclease (8- to 10-fold inhibition) or actinomycin D (twofold inhibition). By contrast, rifampin has little, if any effect. The enzyme(s) synthesizes two primary products, a ribonucleic acid (RNA):DNA hybrid and DNA which is free of RNA. The results of both zonal and equilibrium centrifugation indicate that nascent chains of DNA are associated with the 70S viral RNA. It is concluded that at least two enzymatic activities are under study: transcription of DNA from viral RNA, and subsequent, additional synthesis of DNA, utilizing product of the initial reaction as template.

Avian Leukosis Virus↗