title: Cap-binding protein 1-mediated and eukaryotic translation initiation factor 4E-mediated pioneer rounds of translation in yeast.
abstract: Nonsense-mediated mRNA decay (NMD) in mammalian cells is restricted to newly synthesized mRNA that is bound at the 5' cap by the major nuclear cap-binding complex and at splicing-generated exon-exon junctions by exon junction complexes. This messenger ribonucleoprotein has been called the pioneer translation initiation complex and, accordingly, NMD occurs as a consequence of nonsense codon recognition during a pioneer round of translation. Here, we characterize the nature of messenger ribonucleoprotein that is targeted for NMD in Saccharomyces cerevisiae. Data indicate that NMD targets both cap-binding complex (Cbc)1p- and eukaryotic translation initiation factor (eIF)4E-bound mRNAs, unlike in mammalian cells, where NMD does not detectably target eIF4E-bound mRNA. First, intron-containing pre-mRNAs in yeast are detectably bound by either Cbc1p, or, unlike in mammalian cells, eIF4E, indicating that mRNAs can be derived from either Cbc1p- or eIF4E-bound pre-mRNAs. Second, the ratio of nonsense-containing Cbc1p-bound mRNA to nonsense-free Cbc1p-bound mRNA, which was < 0.4 for those mRNAs tested here, is essentially identical to the ratio of the corresponding nonsense-containing eIF4E-bound mRNA to nonsense-free eIF4E-bound mRNA, and both ratios increase in cells treated with the translational inhibitor cycloheximide (CHX). These data, together with data presented here and elsewhere showing that Cbc1p-bound transcripts are precursors to eIF4E-bound transcripts, demonstrate that Cbc1p-bound mRNA is targeted for NMD. In support of the idea that eIF4E-bound mRNA is also targeted for NMD, eIF4E-bound mRNA is targeted for NMD in strains that lack Cbc1p. These results suggest that both Cbc1p- and eIF4E-mediated pioneer rounds of translation occur in yeast.
authors.affiliation: Department of Biochemistry and Biophysics, University of Rochester Medical Center, 601 Elmwood Avenue, Box 712, University of Rochester, Rochester, NY 14642, USA.
authors.forename: Qinshan
authors.initials: Q
authors.lastname: Gao
authors.forename: Biswadip
authors.initials: B
authors.lastname: Das
authors.forename: Fred
authors.initials: F
authors.lastname: Sherman
authors.forename: Lynne E
authors.initials: LE
authors.lastname: Maquat
mesh_terms: D001483:Base Sequence; D003513:Cycloheximide / Q000494:pharmacology; D004271:DNA, Fungal / Q000235:genetics; D039561:Eukaryotic Initiation Factor-4E / Q000235:genetics / Q000378:metabolism*; D005294:Ferrochelatase / Q000235:genetics / Q000378:metabolism; D005800:Genes, Fungal; D008954:Models, Biological; D014176:Protein Biosynthesis / Q000187:drug effects; D039381:RNA Cap-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D012322:RNA Precursors / Q000235:genetics / Q000378:metabolism; D012331:RNA, Fungal / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D004271:DNA, Fungal; D039561:Eukaryotic Initiation Factor-4E; D039381:RNA Cap-Binding Proteins; D012322:RNA Precursors; D012331:RNA, Fungal; D012333:RNA, Messenger; D029701:Saccharomyces cerevisiae Proteins; D003513:Cycloheximide; C103747:MET8 protein, S cerevisiae; D005294:Ferrochelatase