Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.30.1 (S1 nuclease)
 3,660 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The mouse dihydrofolate reductase gene (dhfr) is a housekeeping gene expressed under the control of a promoter region embedded in a CpG island--a region rich in unmethylated CpG dinucleotides. A divergent transcription unit exists immediately upstream of the dhfr gene which is coamplified with dhfr in some but not all methotrexate-resistant cell lines. We show that the promoter region for this gene pair consists of two bidirectional promoters, a major and minor promoter, which are situated within a 660-base-pair region upstream of the dhfr ATG translation initiation codon. The major promoter controls over 90% of dhfr transcription, while the minor promoter directs the transcription of the remaining dhfr mRNAs. The major promoter functions bidirectionally, transcribing a divergent 4.0-kilobase poly(A) mRNA (class A) in the direction opposite that of dhfr transcription. The predicted protein product of this mRNA is 105 kilodaltons. The minor promoter also functions bidirectionally, directing the transcription of at least two divergent RNAs (class B). These RNAs, present in quantities approximately 1/10 to 1/50 that of the class A mRNAs, are 4.4- and 1.6-kilobase poly(A) mRNAs. cDNAs representing both class A and class B mRNAs have been cloned from a mouse fibroblast cell line which has amplified the dhfr locus (3T3R500). DNA sequence analysis of these cDNAs reveals that the class A and class B mRNAs share, for the most part, the same exons. On the basis of S1 nuclease protection analysis of RNA preparations from several mouse tissues, both dhfr and divergent genes showed similar levels of expression but did show some specificity in start site utilization. Computer homology searches have revealed sequence similarity of the divergent transcripts with bacterial genes involved in DNA mismatch repair, and we therefore have named the divergently transcribed gene Rep-1.
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PMID:Dual bidirectional promoters at the mouse dhfr locus: cloning and characterization of two mRNA classes of the divergently transcribed Rep-1 gene. 267 79

The human dihydrofolate reductase (DHFR) gene was found to be undermethylated only in its 5' promoter region; the remaining CCGG residues in the 30-kilobase (kb) DHFR gene were insensitive to digestion by HpaII. Each of 27 CpG residues that were part of an HpaII or HhaI cutting site within a 1.1-kb segment of the DHFR gene promoter region were found to be unmethylated. All 80 copies of the DHFR gene in methotrexate-resistant HeLa cell line exhibited this pattern of undermethylation of only the promoter region. This same region was shown to be DNase I hypersensitive in chromatin from normal cells and from those cells in which the DHFR gene was amplified. Again, all copies of the amplified gene exhibited DNase I hypersensitivity of the promoter region. The remainder of the 30-kb DHFR gene is both completely methylated and insensitive to DNase I digestion. Detailed mapping of the DNase I-hypersensitive region revealed four strong cutting sites within a 500-base pair segment immediately upstream from the DHFR coding sequence and a weak cutting site within intron I. Two of the strong DNase I cutting sites in chromatin were also sensitive to S1 nuclease nicking when this DNA fragment was part of supercoiled plasmid DNA. Promoter undermethylation and DNase I hypersensitivity, features previously shown for specialized and inducible genes, have now been shown to be characteristic of the constitutively expressed DHFR gene. That these features characterize all copies of the amplified DHFR gene in a methotrexate-resistant cell line suggest that all gene copies are transcriptionally active.
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PMID:Only the promoter region of the constitutively expressed normal and amplified human dihydrofolate reductase gene is DNase I hypersensitive and undermethylated. 298 20

Using primer extension and nuclease S1-mapping techniques we have re-examined the 5' termini of RNA transcribed from the mouse dihydrofolate reductase gene. We characterize a previously undescribed transcription initiation site at position -55 relative to the AUG codon, in addition to the previously identified start site at position -115. Differences in the 5' noncoding regions of these two transcripts with respect to their length and relative G + C content result in their differential ability to form stable hybrids with the DNA probe used in previous analyses of these transcripts and thus precluded the detection of transcripts initiated at -55. We show that changes in the temperature of the hybridization reaction result in the ability to detect the RNA having a shorter noncoding region and a lower G + C content. That position -55 represents an authentic transcription start site is confirmed by use of a DNA probe with which the two transcripts can form S1-resistant hybrids of equal stability and by primer extension analysis using an oligonucleotide primer that hybridizes near the AUG codon. These analyses also demonstrate that the transcript with a 5' end mapping near position -55 accounts for the majority of cellular dihydrofolate reductase RNA.
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PMID:A re-examination of the 5' termini of mouse dihydrofolate reductase RNA. 300 71

Quantitative S1 nuclease mapping studies were performed with uniformly labeled RNA probes, containing contiguous dihydrofolate reductase exon and intron sequences, and total RNA isolated from KB7B cells exposed to 5-fluorouracil for 5 days. Dihydrofolate reductase RNA containing both exon 1 and intron I, or exon 5 and a portion of intron V, increased up to 5-fold in cells grown in the presence of 2.0 to 3.0 microM 5-fluorouracil. Dihydrofolate reductase RNA containing exon 1 or exon 5, but lacking intron I or intron V, respectively, increased 2-fold in cells grown in the presence of 0.65 to 3.0 microM 5-fluorouracil. Primer extension analysis and S1 mapping studies revealed two major transcriptional start sites at positions -72 and -69 and minor start sites upstream from position -183, for dihydrofolate reductase RNA isolated from methotrexate-resistant KB7B cells. The results of these studies demonstrate that 5-fluorouracil alters the metabolism of dihydrofolate reductase precursor mRNA and/or processing intermediates.
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PMID:5-Fluorouracil augmentation of dihydrofolate reductase RNA containing contiguous exon and intron sequences in KB7B cells. 303 31

The 5' structure of mRNA transcribed from the dihydrofolate reductase-thymidylate synthase (DHFR-TS) gene of the protozoan parasite Leishmania major has been characterized. S1 nuclease mapping identifies a heterogenous 5' structure which is not affected by growth phase or developmental stage. The DNA sequence of the 5' region of the DHFR-TS gene does not reveal homology with other trypanosomatid genes, eukaryotic consensus genetic elements, or the mammalian DHFR promoter element. This latter finding is especially significant as we show that the 5' region of the E. coli DHFR gene exhibits homology to the mammalian DHFR promoter element, despite their greater evolutionary distance.
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PMID:Sequence and S1 nuclease mapping of the 5' region of the dihydrofolate reductase-thymidylate synthase gene of Leishmania major. 355 43

A new method, utilizing selective photodegradation of 5-bromo-deoxyuridine (BUdR)-substituted DNA and flow cytometry, has been developed for analyzing the timing of replication of specific DNA sequences. Chemically synchronized Chinese hamster ovary cells were given a pulse of the deoxythymidine analogue, BUdR, at different times during S phase, and flow sorted according to DNA content, before DNA isolation. Newly-replicated, unifilarly BUdR-substituted DNA was selectively degraded by treatment with 33258 Hoechst plus near UV light followed by S1 nuclease digestion; the resistant DNA was analyzed for its content of 18s and 28s rDNA or dihydrofolate reductase (DHFR) sequences via Southern blot analysis. Both the rDNA and DHFR sequences were found to replicate almost entirely during the first quarter of S phase. The approach described should have general utility for analyzing replication kinetics of specific DNA sequences in mammalian cells.
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PMID:High resolution analysis of the timing of replication of specific DNA sequences during S phase of mammalian cells. 619 92

Resistant strains for trimethoprim, a potent inhibitor of dihydrofolate reductase, were obtained by transforming the ligated products of Escherichia coli K12 DNA and plasmid pBR322 BamH I fragments. The strains carry a 13.6 kbp plasmid, pTP1, which contains the trimethoprim- and ampicillin-resistance determinant genes. The trimethoprim-resistance determinant gene was estimated to consist of more than 500 nucleotides and less than 1,500 nucleotides and was restricted by EcoR I and Sal I. Trimethoprim-, ampicillin-, and tetracycline-resistant plasmids were made in the following way, and the resultant plasmids contained a unique EcoR I "insertional inactivation" site for trimethoprim resistance: the DNA sequences extraneous to the determinant gene of the trimethoprim resistance on BamH I fragment of pTP 1 were eliminated by digestion with a double-strand-specific exonuclease BAL 31, and the resultant fragments were ligated with pBR 322 which had been digested by EcoR I and a single-strand-specific nuclease S1. The strains carrying pTP 1 or trimethoprim-resistant plasmids produced about 10 times more dihydrofolate reductase than control strains. The enhancement of the enzyme production, which is due to an increase in the copy number of the enzyme gene, seems to be responsible for the trimethoprim resistance of the transformed cells.
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PMID:Cloning of dihydrofolate reductase gene of Escherichia coli K12. 704 10

The untranslated first exon and the 5'-flanking region for the rat liver NADPH-cytochrome P450 oxidoreductase gene has been isolated from a Wistar-Furth genomic library. The remainder of the gene is composed of 15 exons which code for the mature protein and a 3'-nontranslated segment (T. D. Porter et al. Biochemistry, 1990, 29, 9814-9818). The 56-bp first exon resides 30.5 kb upstream from exon two, making the total gene length approximately 50 kb. While the region surrounding the start site (TCAGAGAC) was found to be homologous to a eukaryotic cap signal, the 5' flanking region possesses neither a TATA nor a CCAAT box. Instead it contains five GC-rich hexanucleotide consensus sequences for the transcription factor Sp1. These features clearly distinguish it from genes encoding other members of the mixed-function oxidase system, the cytochromes P450. Primer extension analysis and S1 nuclease mapping identified multiple transcriptional start sites. In many respects, the TATA-less oxidoreductase promoter resembles the promoter regions of dihydrofolate reductase and other housekeeping genes. Northern blot analysis demonstrates that this promoter is modulated by phenobarbital and trans-stilbene oxide, known inducers of oxidoreductase.
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PMID:NADPH cytochrome P-450 oxidoreductase gene: identification and characterization of the promoter region. 817 32

A quantitative polymerase chain reaction (PCR) assay has been developed to determine the absolute and relative amounts of each dihydrofolate reductase RNA species present at different stages of splicing (i.e., pre-mRNA, splicing intermediate, and mRNA). The ratios of each RNA species as measured by quantitative PCR have been confirmed by S1 nuclease mapping analysis. Quantitative PCR studies reveal a concentration-dependent decrease in the levels of dihydrofolate reductase mRNA and a splicing intermediate but little change in pre-mRNA levels after long term exposure of cells to 5-fluorouracil (FUra). The observed changes correlate with the extent of FUra incorporation into RNA and with cytotoxicity. These results, together with previous data from our laboratory, provide the first direct evidence that FUra incorporation into RNA can cause inhibition of pre-mRNA splicing in vivo. Inhibition of pre-mRNA splicing is thus a likely additional mechanism by which FUra incorporation into RNA may lead to growth inhibition and cell death.
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PMID:5-Fluorouracil alters dihydrofolate reductase pre-mRNA splicing as determined by quantitative polymerase chain reaction. 834 Dec 75