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Results for “RNA-Directed DNA Polymerase”

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PubMedDate not supplied

[Reproduction of leukovirus RD-114 in diploid and heteroploid human cells].

The capacity of leukovirus RD-114 to replicate in human embryo lung diploid cell cultures and continuous human angiosarcoma cell cultures (AS and 709 lines). Differences in the capacity to support the virus reproduction were observed in the two strains of human embryo lung cells (HEL-1 and HEL-3) and the two continuous angiosarcoma cell lines. No virus reporduction was observed in mouse and rat cell cultures. No cytopathic or transformation changes were caused by the virus in any of the systems examined.

Animals↗
PubMed1975

Acute myelogenous leukemia of the Wistar/Furth rat: establishment of a continuous tissue culture line producing lysozyme in vitro and in vivo.

A transplantable myelogenous leukemia of an inbred Wistar/Furth rat has been established in tissue culture and cloned. The resulting transplantable leukemia line demonstrates in vitro doubling time of 20 hr, colony-forming efficiency of 5% in liquid and methylcellulos-containing medium, and a saturation density of 3.0 x 106 cells/sq cm in liquid medium. Following intraperitoneal inoculation, newborn rats developed solid tumors, ascities, and leukemia with ld50 of5 x 103 cells and mean latency of 60 days. The tumor cell morphology was consistent with that of acute myelogenous leukemia. Histochemical staining for myeloid enzymes revealed no evidence of myeloperoxidase, esterase, or leukocyte alkaline phosphatase; however, fluorescent antibody staining for lysozyme was markedly positive. Serum, urine, and ascitic fluid from rats with transplanted leukemia also contained elevated levels of lysozyme. There was no detectable type-CRNA virus production by this cell line after as long as 100 days in vitro. This inbred rat myelogenous leukemia should provide a useful model for studies of chemotherapy and immunoltherapy of human acute myelogenous leukemia.

Animals↗
PubMed1975

Possible association of oncornavirus type D with some forms of human cancer.

The method of molecular hybridization of nucleic acids of oncornavirus type D produced by HEp2 cells with cellular nucleic acids was applied. No sequences homologous to the viral nucleic acids were found in normal human embryo cells as well as in bovine, porcine, murine, and chicken cells. No such sequences were found in tissues of malignant lymphomas. Sequences homologous to the viral nucleic acids were found in some cancer cells, predominantly in hormone-associated tumors of females.

Animals↗
PubMed1975

Molecular hybridization study of cells producing oncornaviruses type D.

Five human cell lines producing oncornaviruses type D were studied by the method of molecular hybridization of viral and cellular nucleic acids. Repeated sequences of viral genome equivalents were found in nuclear DNA and numerous copies of viral genome were found in the cytoplasm. The viruses produced by the cell lines were found to be identical or closely related as regards nucleotide sequences of their genomes.

Animals↗
PubMed1975

Effects of nitrosocarbaryl on BALB/3T3 cells.

Carbaryl(N-methyl-1-naphthylcarbamate) and its nitrosated product, N-nitrosocarbaryl, were tested for their effects of BALB/3T3 (clone A31) cells in culture. Nitrosocarbaryl, but not carbaryl, caused transformation of the BALB/3T3 fibroblasts, but neither chemical induced the complete expression of endogenous murine leukemia virus. Transformed cells differed from the parental control cells by loss of contact inhibition, change in morphology, growth in soft agar, growth to higher saturation densities, and tumorigenicity in normal newborn and irradiated weanling mice and athymic (nude) mice. Transformed clones were found to be negative for expression of RNA tumor virus antigens, viral reverse transcriptase, and infectious virus. Thus, it appears that nitrosocarbaryl can transform BALB/3T3 cells to tumorigenic cells with altered biological properties but without complete activation of RNA tumor viruses in the transformed cells. Expression of viral antigen in the transformed cells was inducible by iododeoxyuridine, indicating that the endogenous viral genome was retained in an unexpressed state.

Animals↗
PubMed1975

Partial characterization of C-type particles in a cell line (WR-9) derived from a rat epidermoid carcinoma of spontaneous origin.

A C-type virus continuously released from a cell line (WR-9) derived from a spontaneous epidermoid carcinoma was purified by means of large-scale tissue culture techniques and high-volume zonal centrifuges. With the use of relatively pure virus concentrates, partial characterization of the virus has been accomplished. Up to 60 liters of spent culture medium from relatively low virus-yielding cultures were processed at a time through the Model K ultracentrifuge in order to obtain quantities of virus sufficient for convenient Tween-ether extraction of the major polypeptide (30,000 daltons). This structural protein having group-specific reactivity was purified and isolated by isoelectric-focusing techniques. A UV absorption peak (A280) was found to be coincident with a major peak of radioacticity at pH 8.6, the isoelectric point (pI) for rat virus gs antigen previously reported by other investigators. Because species-specific (gs-1) and cross-reactive (gs-3) determinants coexist on this protein, fractions containing the group-specific antigen were identified on the basis of the mammalian interspecies determinant (gs-3), using antiserum prepared against Tween-ether-disrupted feline leukemia virus. At the same time, reactivity to the gs-1 determinants in identical fractions was observed in complement fixation and gel diffusion assays, using guinea pig antiserum known to contain principally antibodies to rat gs-1 determinants. Presently, the principal source of rat type C viral gs antigen is rat cell line MSB, which continuously releases a rat leukemia virus pseudotype of murine sarcoma virus. The WR-9 rat virus line may be of use in providing an additional source of C-type particles that are capable of yielding good gs reagents.

Animals↗
PubMed1975

An endogenous oncornavirus of guinea pigs: its expression in leukemic cells.

Guinea pigs do not have any known infectious oncornaviruses. We have recently activated an endogenous oncornavirus (GPV) from cultured guinea pig cells after bromodeoxyuridine riboside (BUdR) treatment. GPV is noninfectious for guinea pig cells and is inducible from any guinea pig cell in culture. Although the morphogenesis of the activated virus is unique, it has the morphology and density (1.16 g/ml) of type C oncornaviruses. It contains an oncornavirus specific reverse transcriptase and a high molecular weight RNA (70S) which dissociates into 36S following denaturation. GPV contains 5 major protein components (mol. wt. 95,000 to 16,000 daltons), 2 of which are glycoproteins. The viral genome which remains repressed in normal cells is expressed in leukemic guinea pig cells. These leukemic cells contain particles which have the morphological and biochemical characteristics of BUdR activated endogenous viruses. Unlike the cells transformed by infectious oncornaviruses, the leukemic cells contain the same amount of virus specific DNA present in normal cells.

Animals↗
PubMed1975

Regulation of blood cell diferentiation.

The hemopoietic (blood forming) system contains pluripotent stem cells able to give rise to a variety of differentiated progeny, including erythrocytes, granulocytes, megakaryocytes, monocytes, macrophages, and possible other cell types. Although a good deal is known about cell lineage relationships in the hemopoietic system, only limited information is available about the mechanisms regulating the proliferation and differentiation of the stem cells and their progeny. An approach to this latter problem has been provided by the develoment of new techniques for the cultivation of hemopoietic cells in short-term cultures. In such cultures, the proliferation and differentiation of hemopoietic cells can be studied under controlled conditions. Two areas of investigation show particular promise: elucidation of the role of the cell surface membrane in regulation; and the possible development, through a detailed investigation of the properties of leukoviruses, of new methods for the genetic analysis of hemopoietic cells.

Animals↗
PubMedDate not supplied

[Effect of synthetic polynucleotides and RNA on poly(C)-dependent poly(G) polymerase activity of Q beta replicase].

The effect of synthetic polynucleotides and phage RNA on poly(C)-dependent synthesis of poly (G) by Qbeta replicase is studied. It is shown that single stranded poly(U) and poly (dT) are strong inhibitors whereas structured polynucleotides poly(A), MS2 RNA as well as double stranded complexes poly(A)-poly(U) and poly(A)-poly(dT) do not affect the synthesis of poly(G). It is suggested that contact region of template with enzyme has single stranded unhelical structure and affinity of polynucleotides to Qbeta replicase is determined by degree of their secondary structure.

Kinetics↗
PubMed2024

PTGS is dispensable for the initiation of epigenetic silencing of an active transposon in Arabidopsis.

Transposable elements (TEs) are repressed in plants through transcriptional gene silencing (TGS), maintained epigenetic silencing marks such as DNA methylation. However, the mechanisms by which silencing is first installed remain poorly understood in plants. Small interfering (si)RNAs and post-transcriptional gene silencing (PTGS) are believed to mediate the initiation of TGS by guiding the first deposition of DNA methylation. To determine how this silencing installation works, we took advantage of ÉVADÉ (EVD), an endogenous retroelement in Arabidopsis, able to recapitulate true de novo silencing with a sequence of PTGS followed by a TGS. To test whether PTGS is required for TGS, we introduce active EVD into RNA-DEPENDENT-RNA-POLYMERASE-6 (RDR6) mutants, an essential PTGS component. EVD activity and silencing are monitored across several generations. In the absence of PTGS, silencing of EVD is still achieved through installation of RNA-directed DNA methylation (RdDM). Our study shows that PTGS is dispensable for de novo EVD silencing. Although we cannot rule out that PTGS might facilitate TGS, or control TE activity, initiation of epigenetic silencing can take place in its absence.

Arabidopsis↗