title: 5-Fluorouracil augmentation of dihydrofolate reductase RNA containing contiguous exon and intron sequences in KB7B cells.
abstract: 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.
mesh_terms: D004720:Endonucleases; D005091:Exons / Q000187:drug effects*; D005472:Fluorouracil / Q000494:pharmacology*; D006801:Humans; D007438:Introns / Q000187:drug effects*; D007624:KB Cells; D009694:Nucleic Acid Precursors / Q000235:genetics; D009710:Nucleotide Mapping; D012322:RNA Precursors; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics*; D015719:Single-Strand Specific DNA and RNA Endonucleases; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics*
chemical_list: D009694:Nucleic Acid Precursors; D012322:RNA Precursors; D012333:RNA, Messenger; D013762:Tetrahydrofolate Dehydrogenase; D004720:Endonucleases; D015719:Single-Strand Specific DNA and RNA Endonucleases; D005472:Fluorouracil