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)

Megaloblastic anaemia is due to a derangement of DNA synthesis caused by insufficient supply of one or other of the four deoxyribonucleoside triphosphate (dNTP) precursors of DNA synthesis or by direct inhibition of one or other DNA polymerase. Reduced supply of the pyrimidine deoxythymidine triphosphate (dTTP) may be caused by folate or vitamin B12 deficiencies or by the action of dihydrofolate reductase inhibitors (e.g. methotrexate, pyrimethamine or trimethoprim), all of which cause reduced supply of the coenzyme 5, 10 methylene tetrahydrofolate (pentaglutamate) needed for thymidylate synthetase. Reduced dTTP supply may also be caused by direct inhibition of thymidylate synthetase by 5-fluorouracil. Reduced supply of both purines, deoxyadenosine triphosphate (dATP) and deoxyguanosine triphosphate (dGTP), may be caused by hydroxyurea, 6-mercaptopurine (and probably by another purine antagonist azaserine), whilst reduced supply of both pyrimidine DNA precursors, dTTP and dCTP (deoxycytidine triphosphate) may be due to inherited orotic aciduria or to treatment with azauridine. Cytosine arabinoside directly inhibits DNA polymerase. DNA replication is a discontinuous process and a number of enzymes are concerned with different aspects of the process. The parental strands partly unwind and a large number of initiation points or origins are activated on both strands. A primer RNA is first synthesised using the parental strand of DNA as template. Fragments of new DNA are then synthesised on the parental DNA template, starting at the RNA primer, under the action of one or other DNA polymerase (probably gamma). The RNA primer is then removed and the gap left is filled by further DNA synthesis under the action of a different DNA polymerase (probably alpha). The fragments of new DNA are joined to give newly synthesised stretches of DNA (replicons) which are then liigated together to form bulk DNA of enormous molecular weight. It is suggested here that reduced supply of one or other of the four deoxyribonucleoside triphosphate (dNTP) during the 'S' phase of the cell cycle (due to vitamin B12 or folate deficiency, drug treatment or other congenital or acquired abnormality in synthesis of the dNTP) impairs the cell's ability to elongate newly initiated DNA fragments by preventing gap-filling, the polymerase needed for gap-filling requiring substantially greater concentrations of the deoxyribonucleoside triphosphates than the polymerase involved in chain initiation. Cytosine arabinoside, which also may cause megaloblastosis, may affect principally the synthesis of new DNA fragments. Since active protein synthesis is needed for the cell to enter the S phase and RNA synthesis is needed to prime new DNA synthesis, megaloblastic anaemia may be expected to occur only when DNA synthesis is inhibited but protein and RNA synthesis are relatively unimpaired...
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PMID:Vitamin B12--folate interrelations. 1 Jan 22

DNA synthesis has been studied in nuclei isolated from phytohaemagglutinin-stimulated lymphocytes from normal subjects and patients with megaloblastic anaemia. Lymphocytes were incubated for 72 h, nuclei isolated and incorporation of tritiated deoxythymidine triphosphate ([3H]TTP) into DNA measured, usually over a 10 min incubation period. Preincubation of normal phytohaemagglutinin-stimulated lymphocytes with methotrexate (1 - 10(-5) M, 48--72 h), 5-fluorouracil (1 - 10(-6) M, 70--72 h), and 1-beta-D-arabinofuranosyl cytosine (cytosine arabinoside) (4 - 10(-5) M, 71--72 h) caused a mean rise in [3H]TTP incorporation of 1.7 (P less than 0.01), 1.7 (P less than 0.05) and 2.4 (P less than 0.0025) fold, respectively. Hydroxyurea (3 - 10(-4) M, 48--72 h) in two experiments caused a mean increase of 1.6 fold. Untreated vitamin B-12- and folate-deficient cells showed a 2.0-fold (P less than 0.05) increase above the incorporation when the deficiencies were corrected by addition of vitamin B-12 and folic acid between 0 and 72 h in vitro. The mean percentages of the incorporation due to ATP-independent synthesis in nuclei from normal untreated cells, 5-fluorouracil-treated, cytosine arabinoside treated and vitamin B-12- or folate-deficient cells were 56 +/- 7% S.E., 41 +/- 7%, 84 +/- 3% and 28 +/- 6%, respectively. 5-Fluorouracil caused a two-fold increase in the cytoplasmic fraction of DNA polymerase when added to phytohaemagglutinin-stimulated lymphocytes between 48 and 72 h of culture but had no significant effect when added between 70 and 72 h.
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PMID:DNA synthesis in isolated lymphocyte nuclei. Effects of megaloblastic anaemia due to folate or vitamin B-12 deficiency or antimetabolite drugs. 88 15

The activities of 5-methyltetrahydrofolate (5-CH3THF) related enzymes and DNA polymerase alpha were determined in bone marrow cells obtained from patients with vitamin B12 deficient megaloblastic anemia and compared with those from healthy volunteers and patients with hemolytic anemia. 5-CH3THF homocysteine methyltransferase activity was significantly lower than that in the control subjects. 5,10-methylenetetrahydrofolate reductase activity was only slightly elevated to that in the control subjects. DNA polymerase alpha activity was significantly higher than that in the control. High deoxyuridine suppression test values in vitamin B12 deficient bone marrow cells were improved by tetrahydrofolate, but not by 5-CH3THF. These data indicate that, even though the reverse reaction catalyzed by 5,10-methylenetetrahydrofolate reductase may be operative in vitamin B12 deficiency, it is not sufficient to correct the disturbance in folate metabolism in vitamin B12 deficiency. Increased DNA polymerase alpha activity may be due to compensation for disarranged DNA synthesis.
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PMID:5-Methyltetrahydrofolate related enzymes and DNA polymerase alpha activities in bone marrow cells from patients with vitamin B12 deficient megaloblastic anemia. 703 72