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)

Cultured Chinese hamster ovary (CHO) cells were treated with the polycyclic aromatic hydrocarbon racemic 3 alpha,4 beta-dihydroxy-1 alpha,2 alpha-epoxy-1,2,3,4- tetrahydrobenzo[c]phenanthrene. Mutants deficient in dihydrofolate reductase activity were isolated. A carcinogen treatment at 0.1 microM yielded at 46% survival of the treated population and an induced frequency of mutation of 1.7 x 10(-4), 10(3)-fold greater than the spontaneous rate. By polymerase chain reaction amplification and direct DNA sequencing, we determined the base changes in 38 mutants. Base substitutions accounted for 78% (30/38) of the mutations. We obtained, in addition, four frameshift and four complex mutations. The preferred type of mutation was transversion (A.T----T.A and G.C----T.A) occurring in 69% of the analyzed mutants. A purine was on the 3' side of the putative adduct site in every mutant. Mutations were favored at sequences AGG, CAG, and AAG (the underlined base is the target). Surprisingly, 42% of the mutations created mRNA splicing defects (16/38), especially at splice acceptor sites for each of the five introns. Thus, this chemical carcinogen may recognize some aspect of DNA structure in regions corresponding to pre-mRNA splice sites.
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PMID:Splicing mutations in the CHO DHFR gene preferentially induced by (+/-)-3 alpha,4 beta-dihydroxy-1 alpha,2 alpha-epoxy-1,2,3,4- tetrahydrobenzo[c]phenanthrene. 237 Dec 81

In a previous report it was shown that mammalian ribosomes were capable of initiating translation at a non-AUG triplet when the initiation codon of mouse dihydrofolate reductase (dhfr) was mutated to ACG (Peabody, D.S. (1987) J. Biol. Chem. 262, 11847-11851). In order to assess the capacity of the mammalian translation apparatus to initiate at other non-AUG triplets, the initiator AUG of dihydrofolate reductase was converted to GUG, UUG, CUG, AGG, AAG, AUA, AUC, and AUU. These represent (with ACG) all the possible triplets that differ from AUG by only one nucleotide. The ability of each mutant to produce dihydrofolate reductase was assessed by in vitro transcription/translation of the mutant dhfr sequences under control of the bacteriophage SP6 promoter. Each of the triplets (with the exceptions of AGG and AAG) was able to direct the synthesis of apparently normal dihydrofolate reductase. Incorporation of [35S]tRNAifMet into the products of in vitro translation indicates that in each case the non-AUG triplet is able to direct initiation of the polypeptide chain with methionine. The mutant dhfr sequences were also inserted into the mammalian expression vector SVGT5 for expression in cultured monkey cells. The hierarchy of relative translation efficiencies was similar in vivo and in vitro.
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PMID:Translation initiation at non-AUG triplets in mammalian cells. 253 69