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Query: EC:2.7.7.49 (reverse transcriptase)
 31,746 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cells of the established MvlLu mink line spontaneously released a reverse transcriptase-containing virus after long-term passage in tissue culture. By molecular hybridization, DNA of normal mink cells was found to possess extensive nucleotide sequence homology with a reverse-transcription product of the viral genome, demonstrating that the new isolate was an endogenous virus of mink origin. The mink virus shared antigenic determinants with the major structural proteins of known mammalian type C viruses. Double-antibody competition radioimmunoassays were developed by utilizing the purified major structural protein, p30, of the mink endogenous virus. The virus was shown to possess antigenic determinants unique from those of other known mammalian type C viruses. It exhibited a higher degree of immunological cross-reactivity with endogenous rat type C and horizontally transmitted feline leukemia viruses than with other mammalian type C viruses tested. The finding that mink cells can remain nonvirus producing for many cell generations argues that there normally exists some cellular restriction to endogenous virus expression in this species.
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PMID:Isolation and characterization of an endogenous type C RNA virus of mink (Mv1Lu) cells. 7 20

A strategy based on the identification of type-specific antigenic determinants in the transitional products of gag (p15, p12, and p30 proteins), pol (reverse transcriptase), and env (gp70 glycoproteins) genes of mammalian type C viruses has been used to study genetic recombination between these RNA viruses. By this approach, recombinants involving exogenous and endogenous mouse type C viruses have been identified and genetically mapped. Analogous techniques have been applied to investigate the genetic relationships between different classes of endogenous virus that exist within the same mouse cells. Proteins of the inducible class of xenotropic virus were shown to exhibit extensive antigenic homology with the gag but not the env gene products of the ecotropic virus class. Instead, the env gene-coded glycoproteins of the inducible and noninducible xenotropic virus classes possessed striking antigenic relatedness. These results, as well as supporting findings from molecular hybridization, favor the concept that the inducible xenotropic virus of mouse cells arose by a recombinational mechanism involving the progenitors of the other two endogenous virus classes.
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PMID:Genetic recombination between mouse type C RNA viruses: a mechanism for endogenous viral gene amplification in mammalian cells. 7 13

Human VA-2 cells infected with baboon type C virus were cloned and fused to Syrian hamster cells, and 33 primary hybrid colonies were obtained. These cells segregated human chromosomes and retained the complete hamster genome. Assays for type C viral p30 antigen and reverse transcriptase were performed in conjunction with analyses of 30 gene-enzyme systems representing 22 different human chromosomes. The results comfirmed that a gene, Bevi, previously assigned to human chromosome 6, dominantly controls baboon type C virus expression in hybrid cells. Representative hybrid colones were studied by nucleic acid hybridization techniques for the presence of integrated proviral DNA using complementary 3H-DNA transcripts of the baboon viral RNA genome. For each of 12 clones examined, there was a concordance between the presence of human chromosome 6, the presence of baboon type C proviral DNA sequences and virus expression. Clones which segregated chromosome 6 as judged by isozyme and karyological analyses lost detectable proviral DNA sequences and failed to produce virus. No syntenic association between the replication of baboon virus and the presence of 21 other human chromosomes was deteced. We conclude that Bevi is a preferred integration site for the baboon type C provirus in the human genome.
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PMID:A gene (Bevi) on human chromosome 6 is an integration site for baboon type C DNA provirus in human cells. 8 Feb 84

Type C RNA virus(es) was readily released from primary lymphosarcoma cell cultures of WH/J rabbits after induction with halogenated pyrimidines. The virus contained an RNA-directed DNA polymerase and the p30 structural protein. The rabbit virus RNA-directed DNA polymerase and p30 protein shared antigenic homologies with other mammalian type C oncornaviruses but appear to also possess unique antigenic determinants. Normal rabbit liver contained DNA homologous to a 3H-labeled complementary DNA transcript of the rabbit viral genome, indicating that type C viral genetic information is present in at least the WH/J strain of rabbits.
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PMID:Induction of type C RNA virus from cultured rabbit lymphosarcoma cells. 8 Apr 60

Reverse transcriptase and p30 were purified from various retroviruses and the intra- and interspecific interaction between the two proteins were studied. The intraspecific complex stimulates [3H]TMP incorporation into (dT)12.(rA)n severalfold above that of the enzyme itself whereas DNA synthesis in the presence of the interspecific complex can stimulate DNA synthesis about 1.5-fold. The sedimentation rate value of the intraspecies complex varies between 12 and 16 S with an estimated molecular weight of 400,000. The molar ratio of p30:reverse transcriptase within the complex is 8:1. Both complexes can be dissociated into their original protein components by exposure to salt (kcl) solution, except that 0.3 M KCl will dissociate the interspecies complex whereas 0.8 M KCl is required for dissociation of the intraspecies complex. Competition studies in which an interspecies complex was exposed to p30 autologous to reverse transcriptase within the complex resulted in the displacement of the heterologous (p30) protein and the formation of a new intraspecific complex.
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PMID:Effect of RNA tumor virus-specific protein p30 on reverse transcriptase. Intraspecies and interspecies interaction between reverse transcriptase and p30. 8 36

Mouse myeloid leukemic cells which differ in their competence to be induced to differentiate by the normal macrophage- and granulocyte-inducing protein MGI have been used to study the relationship between type C RNA virus production and myeloid cell differentiation. Clones which can be induced by MGI to form Fc and C3 rosettes, to synthesize and secrete lysozyme and to differentiate to mature macrophages and granulocytes (MGI+D+) were induced by MGI to produce higher amounts of type C virus. Clones (MGI+D-) that were less inducible by MGI for Fc and C3 rosettes and lysozyme and were not induced to from mature cells were also less inducible higher virus production. In both types of clones, the increased virus production induced by MGI preceded the induction of rosettes and lysozyme. Clones that were not induced by MGI for rosettes or lysozyme (MGI-D-) showed little or no enhancement of virus production. MGI did not affect virus production in erythroleukemic cells, and erythropoietin did not affect virus production in the myeloid leukemic cells. Dexamethasone, lipopolysaccharide, dimethylsulfoxide and low concentrations of actinomycin D can induce some differentiation-associated properties in some of the clones. With these compounds, there was also a direct relationship between the enhancement of virus production and induction of differentiation-associated properties. Virus released from the three types of clones before or after treatment with MGI or dexamethasone was identified as N-tropic. The enhancement of virus production, as measured by reverse transcriptase activity, was accompanied by an increase in the amount of the viral protein p30, and interferon, which idd not inhibit the induction of differentiation in the myeloid leukemic cells, also did not prevent the increase in the amount of p30. After the early enhancement of virus production associated with the induction of differentiation, a shut-off of virus production occurred in the mature cells induced by MGI in MGI+D+ clones, whereas clones that did not differentiate to mature cells continued to produce virus. The results indicate that enhancement of virus production appears to be an early step in the induction of differentiation. Once induction has occurred, the lack of virus production in the mature cells suggest that a subsequent shut-off of virus production may be required for the completion of differentiation to mature cells. This relationship between cell differentiation and virus production suggests that type C virus has a regulatory role in myeloid cell differentiation.
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PMID:Co-regulation of type C RNA virus production and cell differentiation in myeloid leukemic cells. 8 97

A retrovirus antigenically distinct from known type C, B and D viruses was isolated from normal mink (Mustela vison) lung cells that had been co-cultivated with 5-iododeoxyuridine- and dexamethasone-treated dog mammary tumour cells. Cytogenetic studies of the virus-releasing co-culture showed mitotic figures identical to the normal mink cell line (MvlLu) with the exception of a low frequency of cells with extensive chromosomal breakage and uncoiling. The new virus bands at a buoyant density of 1.16 g/ml, contains 60S RNA and a reverse transcriptase which prefers Mn2+ over Mg2+ for the synthesis of DNA. This enzyme utilizes poly(rA).oligo(dT) more efficiently than poly(dA).oligo(dT) and is also able to synthesize DNA copies from the endogenous RNA. Morphologically, it is a typical type C virus. Filtered virus readily infects mink, dog and other mammalian cells indicating the amphotropic nature of its cell growth requirement. Hybridization studies showed that normal mink DNA contains multiple copies of proviral sequences of this newly isolated virus. Serological analyses indicate that the mink endogenous virus contains in its core protein, in addition to the interspecies type-C determinant, an antigenic component related to one of the determinants found in the feline leukaemia virus p30 protein. This determinant is not present in the Rauscher leukaemia virus, RD114 virus or simian sarcoma virus.
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PMID:Characterization of a retrovirus isolated from normal mink cells co-cultivated with a dog mammary tumour. 8 51

Strains of Friend leukemia virus (FLV) that are associated with polycythemia contain the defective spleen focus-forming virus (SFFV). To determine whether the transforming ability of FLV was affected by the presence of this second agent, DBA/2J mouse bone marrow cells were infected in vitro. Criteria for transformation were the establishment of permanent lines, growth on semisolid agarose, and the production of tumors at the site of inoculation in syngeneic hosts. Two lines of immature hematopoietic cells that grow in suspension originated from the infected cultures. Each has an almost diploid karyotype (38-39 chromosomes) and 3-4 metacentric chromosomes. These transformed cells express gp71 viral envelope glycoprotein and p30 viral core protein antigens. Virus production was measured by reverse transcriptase (RNA-dependent DNA polymerase) activity of the virions released into the medium. The virus, assayed in vivo for infectivity, has SFFV activity but is attenuated for leukemogenicity. The stimulation of hemoglobin synthesis in the cells grown in medium supplemented with dimethyl sulfoxide or hexamethylene bisacetamide indicates that the cells are erythroid in origin. SFFV may have a function analogous to erythropoietin in influencing the process of transformation by FLV.
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PMID:In vitro transformation of mouse bone marrow cells by the polycythemic strain of Friend leukemia virus. 8 91

Several properties of an RNA-directed DNA polymerase associated with a hamster retrovirus (HaRV) were examined and found to be similar to other polymerases from mammalian type-C viruses in that the enzyme (i) is more active with Mn2+ than Mg2+, (ii) uses the reverse transcriptase-specific poly(rCm).oligo(dG) template, (iii) possesses substantial endogenous polymerase activity and (iv) is strongly inhibited by homologous antisera and moderately inhibited by antisera directed against other type-C viruses. In contrast to previous reports of polymerases from other hamster viruses, HaRV polymerase is active in endogenous assays and the activity is associated with a 70,000 mol. wt. polypeptide in highly purified virions and with 70,000 and 85,000 mol. wt. polypeptides in fresh, unpurified virus. Only one major peak of polymerase activity eluted from DEAE-cellulose while subsequent elution of this peak from phosphocellulose produced two major peaks of polymerase activity. The mol. wt. of these two peaks were 70,000 and 85,000 by glycerol density-gradient sedimentation. The HaRV reverse transcriptase and p30 were found to be most closely related antigenically to other rodent retrovirus proteins.
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PMID:Biochemical and immunological properties of the reverse transcriptase associated with a hamster retrovirus. 9 Jan 13

A tissue culture line derived from the Asian rodent Vandeleuria oleracea has been shown to release an infectious, xenotropic type C virus. The virus-associated reverse transcriptase (RNA-dependent DNA nucleotidyltransferase) and the major internal protein p30 are immunologically related to the respective proteins of the woolly monkey-gibbon ape group of infectious primate viruses. By these criteria the V. oleracea viral isolate is similar to the murine type C-I class of endogenous retroviruses and has been designated Vand C-I. Nucleic acid homology studies show that V. oleracea cellular DNA shares similar levels of homology with DNA from members of the Mus and Rattus genera and lower levels of homology with other rodent genera. The Vand C-I viral genome is present in V. oleracea cellular DNA in multiple copies, and partially related sequences can be detected in other rodent genera. These results support the conclusion that the Vand C-I viral genome is genetically transmitted in V. oleracea and that the type C-I class of endogenous retroviral genes has been highly conserved during evolution.
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PMID:Isolation of an endogenous type C virus related to the infectious primate type C viruses from the Asian rodent Vandeleuria oleracea. 9 Jan 55


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