The 5'- and 3'-untranslated regions of ornithine decarboxylase mRNA affect the translational efficiency.
We have determined the roles of the 5'- and 3'-untranslated regions (UTR) of ornithine decarboxylase (ODC) mRNA in the post-transcriptional regulation of this enzyme. A series of expression vectors were constructed in which portions of the ODC 5' and/or 3' UTRs were placed flanking a reporter gene coding sequence, either firefly luciferase or chloramphenicol acetyltransferase, so as to generate a hybrid transcript. Translation of these chimeric genes in transient expression assays in wild type and ODC-deficient hamster cells was examined in the presence of normal or depleted polyamine pools. The ODC 5' UTR suppresses translation of the coding sequence it precedes irrespective of polyamine levels, and this effect is shown to be due to the GC-rich 5' segment of the UTR. The same effect is observed in vivo and in a rabbit reticulocyte in vitro translation system. The GC-rich region has the potential to form a very stable hairpin structure and inhibits translation in a position-dependent but orientation-independent manner. Insertion of the 3' UTR of ODC downstream of the translation termination codon of the reporter gene but prior to the polyadenylation signal partially relieves the suppression of translation imposed by the 5' UTR; the overall translatability of the message improves 30-50-fold.
Grens
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Department of Biology, University of California, San Diego 92093.
Scheffler
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D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D002460:Cell Line; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics; D005822:Genetic Vectors; D008156:Luciferases / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D009690:Nucleic Acid Conformation; D009693:Nucleic Acid Hybridization; D009955:Ornithine Decarboxylase / Q000235:genetics*; D014176:Protein Biosynthesis; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000235:genetics*; D014162:Transfection
D012333:RNA, Messenger; D008156:Luciferases; D015500:Chloramphenicol O-Acetyltransferase; D009955:Ornithine Decarboxylase