Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:4.1.99.3 (PRE)
 1,923 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Escherichia coli DNA photolyase was overproduced and purified from each of two mutant E. coli strains lacking dihydrofolate reductase. The extent of over-production in the mutants was comparable to that seen in the wild type strain. Examination of the isolated photolyase from these strains revealed that the folate cofactor, 5,10-methenyltetrahydrofolate, was present in these proteins at a level of 60-80% compared to that purified from the wild type strain. Further examination of the dihydrofolate reductase-deficient strains revealed the presence of other tetrahydrofolate derivatives. These findings demonstrate that dihydrofolate reductase is not essential for the production of tetrahydrofolates in E. coli.
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PMID:The presence and distribution of reduced folates in Escherichia coli dihydrofolate reductase mutants. 219 Sep 85

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

We have analyzed gene-specific and strand-specific DNA damage and repair in the dihydrofolate reductase gene in hamster cells. Cells were UV-irradiated or treated with two types of chemotherapeutics, alkylating agents or cisplatin. UV-induced pyrimidine dimers were detected using a previously published technique in which the T4 endonuclease V enzyme is used to create nicks at the lesion sites. 6-4 photoproducts were detected in a similar assay using ABC excinuclease after prior reversal of the pyrimidine dimers with photolyase. Adducts formed by the alkylating agents nitrogen mustard and dimethyl sulfate were quantitated by generating strand breaks at basic sites after neutral depurination. Cisplatin-induced intrastrand adducts were detected with ABC excinuclease, and cisplatin interstrand cross-links were detected using a denaturation-reannealing reaction before electrophoresis. In accord with previous reports by other investigators, we find distinct strand specificity of the repair of pyrimidine dimers after UV; the transcribed strand was much more efficiently repaired than the nontranscribed strand. In contrast, there was little or no strand bias in the repair of the 6-4 photoproducts. For alkylating agents, a slight bias toward repair in the transcribed strand was found after treatment with nitrogen mustard, but there appeared to be no bias in the repair after treatment with dimethyl sulfate. Cisplatin interstrand cross-links are repaired with equal efficiency from the two strands, but the more common cisplatin-induced lesion, the intrastrand adduct, is preferentially repaired from the transcribed strand. In conclusion, there is strand bias in the repair of pyrimidine dimers and cisplatin intrastrand adducts, but the strand specificity of repair may not be a general feature for all DNA lesions, as we found little or no strand bias in the repair of other lesions studied.
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PMID:Repair of individual DNA strands in the hamster dihydrofolate reductase gene after treatment with ultraviolet light, alkylating agents, and cisplatin. 842 Sep 40