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:2.7.7.7 (DNA polymerase)
17,007 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We determined that there is a protein in rat liver capable of inhibiting DNA polymerase alpha. To assay for this inhibitor, DNA polymerase alpha was purified from R3230AC rat mammary tumor, a rich source of this enzyme. Protein fractions from Sephacryl S200 gel filtration of total soluble liver extract showing inhibition of DNA polymerase alpha were further chromatographed on DEAE-cellulose. This step revealed two inhibitor protein populations with the major form corresponding to a molecular weight of 143,000 dalton. Soluble extract from isolated rat liver nuclei also showed the presence of at least two inhibitors; the major form was 200,000+ dalton in molecular weight. Both the 143,000 and 200,000+ dalton inhibitor proteins were capable of inhibiting the R3230AC tumor DNA polymerase alpha in a dose-dependent manner. These inhibitors exhibited similar inhibition of nuclear matrix-associated DNA polymerase alpha from either the R3230AC tumor or from regenerating rat liver.
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PMID:Inhibition of DNA polymerase alpha activity by proteins from rat liver. 400 44

Two DNA polymerase with properties of viral RNA-directed DNA polymerase can be found in RIII mouse milk. One enzyme is the polymerase of type-C viruses; this enzyme prefers manganese to magnesium with poly(rA).oligo(dT) as synthetic template, is inhibited by specific sera, and has an apparent molecular weight of 70,000. Milk from BALB/c and NIH Swiss mice contain a vast predominance of this type-C enzyme. The other DNA polymerase from RIII mouse milk prefers magnesium to manganese, is not inhibited by type-C antipolymerase serum, and appears larger on gel chromatography than the type-C viral polymerase. Its presence in milk from RIII mice and absence from milk of mice with low content of mammary tumor virus correlates to the relative degree of type-B virus expression in these mice. The DNA polymerase of Mason-Pfizer monkey virus, isolated from a rhesus monkey breast tumor, also has a marked preference for magnesium with poly(rA).oligo(dT), is not immunologically related to primate type-C viruses, and appears larger than the gibbon type-C enzyme on gel chromatography.
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PMID:Characterization and separation of viral DNA polymerase in mouse milk. 412 83

An in vitro system for production, purification, and concentration of mouse mammary tumor virus is described. Monolayer cultures of C(3)H mouse mammary tumor cells propagated at 34 C in roller bottles in the presence of dexamethasone, a glucocorticoid hormone, release B-type particles which possess ribonucleic acid and a ribonucleic acid-dependent deoxyribonucleic acid polymerase. One thousandfold concentration by ultracentrifugation with subsequent gradient fractionation yielded > 7 x 10(10) particles per ml in the 1.16- to 1.18-g/ml region. Mouse mammary tumor virus produced in this system was free of detectable C-type virus.
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PMID:In vitro system for production of mouse mammary tumor virus. 414 98

Inhibition of the ribonucleic acid (RNA)- and deoxyribonucleic acid (DNA)-dependent DNA polymerase activities of mammalian C-type viruses was obtained with sera from rats bearing murine leukemia virus-induced transplant tumors. Polymerase activities of nonmammalian (viper) C-type virus and murine mammary tumor virus were not inhibited by such sera nor by serum from a rat immunized with the DNA polymerase of feline leukemia virus purified by isoelectric focusing. The latter serum appeared to inhibit preferentially the DNA-dependent DNA polymerase activity of mammalian C-type viruses showing no inhibition of RNA-dependent DNA synthesis.
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PMID:Specific inhibition of mammalian ribonucleic acid C-type virus deoxyribonucleic acid polymerases by rat antisera. 433 48

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

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

We have previously isolated mouse mammary tumor virus (MMTV) host range variants by serial virus passage in feline cells. These variants productively infect cells of a broad range of species but replicate most efficiently in feline cells. We report here the isolation of a series of novel MMTV host range variants that have the ability to replicate with high efficiency in murine, rat, canine and human cells, respectively; these variants were isolated by serial virus passage in cells of each respective species. These new variants, furthermore, all retained their ability to efficiently replicate in feline cells, and each exhibited unique host range properties. The novel MMTV variants obtained from murine, rat, feline, canine, and human cells showed no overt evidence of recombination with endogenous type-C viruses in that they retained their antigenic reactivities in group-specific radioimmunoassays for MMTV polypeptides, and were unreactive for type-C virus proteins when tested by radioimmunoassays and DNA polymerase assays. These novel MMTV host range variants now broaden the spectrum of studies that can be undertaken involving MMTV replication and the initiation and promotion of virus-mediated mammary cell transformation.
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PMID:Isolation of a series of novel variants of murine mammary tumor viruses with broadened host ranges. 624 12

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

We studied the growth capabilities of mammary tumor 13762 transplanted into inbred F344 rats previously cured of tumors by cell kinetically based sequential chemotherapy. Of the 18 challenge tumors, 4 were completely rejected, and nonrejected tumors grew at subnormal rates. The subnormal growth was specific for the cured rats because tumor growth in age- and therapy-matched non-tumor-bearing controls was normal. Cell kinetic studies with the use of in vitro techniques for the [3H]dThd labeling index, DNA synthesis time, and primer-dependent DNA polymerase labeling index (an in vitro estimate of growth fraction) indicated that the subnormal growth rates of the 13762 tumor in cured rats were due to subnormal tumor cell production. Cell loss rates were similar in tumors growing in cured rats and in size-matched tumors growing in normal controls. The results are consistent with the possibility that the subnormal growth of 13762 challenge tumors in chemotherapeutically cured F344 rats was mediated by immune factors.
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PMID:Growth kinetics of mammary tumor 13762 in rats previously cured by chemotherapy. 692 50

We have recently expressed in bacteria an enzymatically active reverse transcriptase (RT) of mouse mammary tumor virus (MMTV), a mammalian retrovirus with a typical B-type morphology [Taube, R., Loya, S., Avidan, O., Perach, M. & Hizi, A. (1998) Biochemical J. 329, 579-587]. The purified recombinant protein was shown to possess the catalytic activities characteristic of retroviral reverse transcriptases. In the present study, we have analyzed two basic parameters characteristic of the DNA polymerase activity of the novel MMTV RT, namely the processivity and the fidelity of DNA synthesis. Two features related to fidelity were studied, the capacity to misinsert wrong nucleotides at the 3' end of the nascent DNA strand and the ability to extend 3' mispairs. The studied properties of MMTV RT were compared with those of the RT purified from virions of avian myeloblastosis virus (AMV), since AMV RT shows a relatively high sequence similarity to MMTV RT. MMTV RT shows a relative processivity of DNA synthesis which is as high as the reference AMV RT. Regarding fidelity of DNA synthesis, MMTV RT shows a fidelity of misinsertion lower than that of AMV RT, whereas its capacity to elongate mispaired DNA is lower than that of AMV RT indicating a somewhat higher fidelity. These fidelity properties are discussed also in the context of the RTs of lentiviruses, especially those of HIV, which were reported to exhibit an exceptionally low fidelity of DNA synthesis. It is clear that MMTV RT has a fidelity higher than that of lentiviral RTs.
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PMID:DNA synthesis exhibited by the reverse transcriptase of mouse mammary tumor virus: processivity and fidelity of misinsertion and mispair extension. 999 Mar 22


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