Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.5.1.3 (dihydrofolate reductase)
 5,819 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

DNA polymerase beta (beta-pol) and its mRNA are maintained at constitutive levels during the cell cycle and during stages of cell growth in culture. To study biological consequences of variations in the level of this DNA repair enzyme and/or its mRNA, we prepared expression vectors in which cDNA for human beta-pol is inserted under the control of a metallothionein promoter (pMT) in the sense and antisense orientation, respectively, and these vectors then were used for stable transformation of mouse 3T3 cells. Vectors also contained the mouse DHFR gene, such that culture of transformants in medium with increasing concentrations of methotrexate resulted in amplification of inserted DNA. The levels of sense and antisense transcripts are strongly increased by culture of transformants in medium with 65 microM Zn2+, although some expression is detected even without Zn2+ induction. After five days of induction, the beta-pol level was about threefold higher in sense cells and about 10-fold lower in antisense cells than in parallel cultures without induction. The antisense line has a threefold increased cell doubling time in the presence of 65 microM Zn2+ compared with the absence of Zn2+. Zn2+ (65 microM) induction for the sense line results in normal growth for the first three days and, thereafter, a complete cessation of growth. Yet, these blocked cells remain fully viable. The results indicate that sudden deregulation of beta-pol expression alters cell growth in mouse 3T3 cells.
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PMID:Deregulation of DNA polymerase beta by sense and antisense RNA expression in mouse 3T3 cells alters cell growth. 169 88

We have developed a method to quantify (6-4) photoproducts in genes and other specific sequences within the genome. This approach utilizes the following two enzymes from Escherichia coli: ABC excinuclease, a versatile DNA repair enzyme which recognizes many types of lesions in DNA, and DNA photolyase, which reverts pyrimidine dimers. DNA is isolated from UV irradiated Chinese hamster ovary cells and digested with a restriction enzyme. Pyrimidine dimers, the major photoproduct produced at biological UV fluences, are then completely repaired by treatment with DNA photolyase. The photoreactivated DNA is treated with ABC excinuclease, electrophoresed in an alkaline agarose gel, transferred to a support membrane and probed for specific genomic sequences. Net incisions produced by ABC excinuclease following photoreactivation are largely due to the presence of (6-4) photoproducts. These adducts are quantitated by measuring the reduction of intensity of the full length fragments on the autoradiogram. Using this approach we have shown that (6-4) photoproducts are produced at equal frequency in the dihydrofolate reductase coding sequence and in its 3'-flanking, noncoding sequences and that the formation of (6-4) photoproducts is linear in both sequences up to a UV dose of 60 J/m2. The repair of (6-4) photoproducts in these DNA sequences was measured after a dose of 40 J/m2 over 4-, 8-, and 24-h time periods. The (6-4) photoproducts are repaired more efficiently than pyrimidine dimers in both sequences and there is preferential repair of (6-4) photoproducts in the dihydrofolate reductase gene compared with the downstream, noncoding sequences.
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PMID:Preferential DNA repair of (6-4) photoproducts in the dihydrofolate reductase gene of Chinese hamster ovary cells. 280 61