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

The RNA-dependent DNA polymerase(s) in murine leukemia, murine mammary tumor, and avian myeloblastosis viruses require maganese for optimal activity. The transcription of added synthetic polyribonucleotides is greatly enhanced when manganese is used in place of magnesium. A soluble RNA-dependent DNA polymerase activity has been released from murine leukemia particles in the presence of manganese and high detergent concentrations. Two RNA viruses, visna virus of sheep and a primate syncytial virus, not known to have tumor-producing ability, also contain the polymerase.
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PMID:RNA-dependent DNA polymerase activity in five RNA viruses: divalent cation requirements. 432 57

Murine leukemia (Rauscher and Moloney strains) and sarcoma (Kirsten strain) virions, as well as the mammary tumor virus of mice, contain an RNA-dependent DNA polymerase. Optimal incorporation of deoxyribonucleoside triphosphates occurs at a critical detergent (Triton X-100) concentration (0.010-0.014%). At higher than optimal detergent concentrations the virion is seen to be disrupted and enzyme activity is lost. The virion, enzymatic activity, and newly synthesized DNA all cosediment in a sucrose gradient. Thus far the enzymatic activity has been found only in RNA viruses that have oncogenic properties.
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PMID:DNA synthesis by RNA-containing tumor viruses. 433 15

An experimental procedure is detailed that permits the detection of 70S RNA-directed DNA synthesis in mouse mammary carcinomas. The DNA synthesized is complementary to the RNA of the mouse mammary tumor virus by molecular hybridization, thus, completing the proof that an RNA-instructed DNA polymerase has been identified. Further, RNA-instructed DNA polymerase and its 70S RNA template are physically associated in a particle that has a density characteristic of oncornaviruses. These experiments now provide the technology required to perform similar examinations of human neoplasias.
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PMID:Detection of RNA-instructed DNA polymerase and high molecular weight RNA in malignant tissue. 434 Jul 47

In mouse cell lines derived from mammary adenocarcinomnas, the synthetic steroid dexamnethasone stimulates production of murine mammary tumor virus. Viral RNA and antigens are increased as much as 20-fold, and culture fluid supernatants from steroid-treated cells contain type B particles with reverse transcriptase. These cells provide a possible tissue culture source of this virus and a model system for studying the mechanism of action of corticosteroids and the regulation of transcription of integrated viral DNA.
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PMID:Dexamethasone stimulation of murine mammary tumor virus expression: a tissue culture source of virus. 436 Oct 99

Mouse mammary tumor virus RNA was transcribed in vitro with avian myeloblastosis virus reverse transcriptase in the presence of calf thymus DNA oligomers. The yield of cDNA was markedly enchanced by increasing the concentration of the enzyme as well as primers in the reaction mixture. The average size of cDNA was approximately 200 residues, and it was not affected by the concentration of deoxynucleoside triphosphates when saturating concentration of enzyme was used. Nearly all of the viral sequences were represented in cDNA and it formed hybrids of high fidelity with viral RNA. Similar results were obtained when murine leukemia virus (AKR) RNA was transcribed. These observations will be useful for synthesizing cDNA of RNAs that are not easily available in sufficient quantities.
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PMID:Synthesis in high yield of complementary DNA of retroviral RNA. 615 40

We have recently established four new human breast cancer cell lines that were characterized as being of human mammary origin. We examined these cell lines for particles morphologically resembling retroviruses by electron microscopy, for extracellular and intracellular particles containing high-molecular-weight RNA and RNA-directed DNA polymerase by biochemical assays, and for mouse mammary tumor virus (MMTV)-related sequences in the cell genomes by molecular hybridization. An extensive search for budding particles by thin-section electron microscopy of cells did not provide evidence for retrovirus-like particles. Similarly, 1000- to 2000-fold concentrated samples of medium harvested from 10(8) cells did not contain particles of a density of 1.14 to 1.16 g/ml containing RNA-directed DNA polymerase. Compared with DNA polymerase activity of MMTV, and taking into account the particle weight and protein content of retroviruses, we estimate that, if these cells produce retrovirus-like particles, this production would be less than 1.6 particles/cell every 24 to 72 hr. The hybridization of cell DNA with MMTV complementary DNA also did not show detectable amounts of virus-related sequences in the cell genome. Analysis of the hybridization results suggested that, if the human breast cells contained MMTV-related sequences, they must be present in less than one copy per 100 cells. Thus, we have obtained no convincing evidence for the presence of retrovirus-like particles or subviral components in these cells. It is of course possible that these cells contain virus information but at levels below the sensitivity of our assay procedures.
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PMID:Search for retrovirus-like particles in human breast cancer cells in culture. 616 39

70S RNA has been prepared from mouse mammary tumor virus (MMTV) produced by the GR tumor cell line. After denaturation for 3 min at 60 degrees C the RNA was applied to a sucrose gradient and molecules sedimenting between 10-16S were selected and passed over an oligo-dT cellulose column. The poly A containing RNA fraction was used as a template for the synthesis of complementary DNA with reverse transcriptase in the presence of dideoxynucleoside triphosphates. Oligo-nucleotides p(dT)7rG, p(dT)7rA and (p(dT)7rC were tested for their primer activity. Two of the three primers gave readable sequences. This suggests a heterogeneity in the 3' end of the viral RNA, a phenomenon also observed with avian retroviruses. Nucleotides 37-45 from the 3' end are made up of only A's and T's and resemble a Hogness box. This finding could have biological consequences for the transcription of proviral DNA in the unintegrated and integrated state. Instead of the usual AAUAAA sequence present in mRNA's close and in front of the site of polyadenylation we find a sequence AGUAAA.
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PMID:Sequence determination of the 3' end of mouse mammary tumor virus RNA. 616 50

The expression of a mouse mammary tumor virus is inducible by hormones, and the virus contains a hormone-responsive element. Viral particles and RNA-directed DNA polymerase (RDDP, EC 2.7.7.7; reverse transcriptase) are both detectable in human breast tumors but the frequency and significance of these findings are unknown. Breast tumor biopsy specimens (from either the primary site or a metastasis), frozen in liquid nitrogen at the time of surgery, were routinely obtained to determine estrogen receptor (ERP) concentration. A sample of the tissue was pulverized, homogenized and centrifuged at low speed to remove nuclei and mitochondria. The supernate was then centrifuged at 225,000 g to obtain the cytosol fraction for estrogen and progestin receptor (PgR) assays. Partially purified membranes for the RDDP assays were prepared from the high-speed pellet by discontinuous sucrose density gradient centrifugation. The RDDP assay involved measuring primer-dependent poly(dT) synthesis in the presence of poly(A) as template and oligo-(dT)12-18 as primer. To date, we have studied biopsy specimens from 46 patients with breast cancer. 27 (59%) had ERP and 23 (50%) were RDDP-positive. There was no significant correlation between ERP concentration and RDDP activity. PgR data were available on 36 of the patients; 17 (47%) were positive. No correlation between RDDP and PgR was apparent. Similarly, there was no correlation between RDDP and clinical stage of the disease.
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PMID:RNA-directed DNA polymerase activity in human breast cancer biopsy specimens. Relation to estrogen receptor protein. 620 38

Human breast cyst fluids were shown to contain low concentrations of IgA (15-78 micrograms/ml) and IgG (33-145 micrograms/ml). The IgA:IgG ratios in individual breast cyst fluids ranged from 1:0.6 to 1:4. These levels are considerably higher than their ratio in serum (1:7). IgA from 33% of the 40 fluids examined, and IgG from 10% of the fluids, reacted with the murine mammary tumor virus (MuMTV). The reactivity was detected by an enzyme-linked immunosorbent assay that measures antibody binding to both the envelope glycoprotein and core protein of the virus. In a second series of experiments. IgA from 28% of 40 breast cyst fluids reacted only with MuMTV while IgA from 30% of the fluids was reactive with both MuMTV and the Rauscher murine leukemia virus. Antigen reactive with antiserum to the 28,000-dalton MuMTV core protein (p28), was also identified in a 165,000-g pellet fraction from breast cyst fluids. In individual fluids, the extent of IgA binding to MuMTV was positively correlated (P less than or equal to 0.01) with the binding of anti-p28 antibody to the pellet of the breast cyst fluid. Fractions with the buoyant density of retroviruses (1.16-1.18 g/ml) or their cores (1.21-1.25 g/ml) were isolated from breast cyst fluids. These fractions contained a DNA polymerase capable of utilizing the reverse transcriptase-specific template, dG12-18 x poly rCm. In addition, they reacted with antiserum to MuMTV p 28 but not with antiserum to the 30,000-dalton Rauscher murine leukemia virus core protein.
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PMID:Antigens and antibodies cross-reactive to the murine mammary tumor virus in human breast cyst fluids. 625 13

Supernatant fluids from cultures of a mouse mammary tumor (MT) cell line were found to produce a specific cell detachment effect when inoculated into HeLa cells. The cell detachment factor (CDG) responsible for this effect was examined. Repeated attempts to cultivate this CDF in bacteriologic, fungal, and mycoplasma media were unsuccessful. However, using the DNA fluorochrome staining technique and specific immunofluorescent staining procedures, the CDF was identified positively as a noncultivable strain of Mycoplasma hyorhinis. It was also noted that this CDF could be labeled with [3H]uridine in MT cell cultures, concentrated, and banded at a density of 1.18 g/cm3 when centrifuged to equilibrium in a 20 to 60% sucrose gradient. Using a multiple antibiotic treatment regimen, the MT cells were "cured" of the M. hyorhinis contaminant. Re-infection of these cells with an exogenous strain of M. hyorhinis resulted in the same cell detachment effect, and this strain when labeled with [3H]uridine also sedimented at a density of 1.18 g/cm3. The salient feature of these studies is that M. hyorhinis sediments at the same density of mouse mammary tumor virus (MMTV) in sucrose density gradients. This was demonstrated by sucrose density gradient analyses of a purified sample of MMTV, assaying for reverse transcriptase activity, and a [3H]uridine labeled sample of the M. hyorhinis present in the MT cell cultures.
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PMID:Covert infection of a mouse mammary tumor cell line with Mycoplasma hyorhinis: cosedimentation with mouse mammary tumor virus in sucrose density gradients. 627 89


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