title: Effects of c-myc first exons and 5' synthetic hairpins on RNA translation in oocytes and early embryos of Xenopus laevis.
abstract: Mammalian c-myc transcripts have long G/C-rich 5' untranslated regions (UTRs) that may fold into secondary structural elements that may impede translation. We have examined the effects of different c-myc first exons, which produce most of the 5' UTR of c-myc transcripts, on translation in Xenopus oocytes and embryos, by placing these structures upstream of a chloramphenicol acetyltransferase (CAT) reporter. Our results demonstrate that the human c-myc first exon inhibits reporter translation in both oocytes and embryos. Unlike their mammalian counterparts, Xenopus c-mycI first exons initiated at either promoter 1 or promoter 2 do not impede translation. We conclude that translation inhibition reported in a previous investigation (Lazarus, 1992. Oncogene, 7:1037) utilizing Xenopus c-mycI 5' non-coding elements was due to the inclusion of nonrelevant non-transcribed sequences. Previous investigators have reported that inhibition of translation in Xenopus oocytes by 5' secondary structure is alleviated after fertilization (Lazarus et al., 1988. Oncogene 3:517; Fu et al., 1991, Science 251:807). We repeated the experiments of Fu et al., examining the effects on translation by a highly stable synthetic hairpin. The hairpin severely [correction of severly] restricted translation in both oocytes and embryos, indicating that highly stable 5' secondary structure is equally inhibitory in oocytes and embryos.
authors.affiliation: Department of Biological Sciences, University of Calgary, Alberta, Canada.
authors.forename: S D
authors.initials: SD
authors.lastname: Fraser
authors.forename: J
authors.initials: J
authors.lastname: Wilkes-Johnston
authors.forename: L W
authors.initials: LW
authors.lastname: Browder
mesh_terms: D000818:Animals; D001483:Base Sequence; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000502:physiology; D005091:Exons; D005260:Female; D016259:Genes, myc; D006801:Humans; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009865:Oocytes / Q000502:physiology; D014176:Protein Biosynthesis; D012313:RNA / Q000235:genetics* / Q000494:pharmacology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D014982:Xenopus laevis / Q000196:embryology*
chemical_list: D012333:RNA, Messenger; D012313:RNA; D015500:Chloramphenicol O-Acetyltransferase