Cap-binding protein 1-mediated and eukaryotic translation initiation factor 4E-mediated pioneer rounds of translation in yeast

Proc Natl Acad Sci U S A. 2005 Mar 22;102(12):4258-63. doi: 10.1073/pnas.0500684102. Epub 2005 Mar 7.

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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Base Sequence
  • Cycloheximide / pharmacology
  • DNA, Fungal / genetics
  • Eukaryotic Initiation Factor-4E / genetics
  • Eukaryotic Initiation Factor-4E / metabolism*
  • Ferrochelatase / genetics
  • Ferrochelatase / metabolism
  • Genes, Fungal
  • Models, Biological
  • Protein Biosynthesis* / drug effects
  • RNA Cap-Binding Proteins / genetics
  • RNA Cap-Binding Proteins / metabolism*
  • RNA Precursors / genetics
  • RNA Precursors / metabolism
  • RNA, Fungal / genetics
  • RNA, Fungal / metabolism
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Saccharomyces cerevisiae / drug effects
  • Saccharomyces cerevisiae / genetics*
  • Saccharomyces cerevisiae / metabolism*
  • Saccharomyces cerevisiae Proteins / genetics
  • Saccharomyces cerevisiae Proteins / metabolism*

Substances

  • DNA, Fungal
  • Eukaryotic Initiation Factor-4E
  • RNA Cap-Binding Proteins
  • RNA Precursors
  • RNA, Fungal
  • RNA, Messenger
  • Saccharomyces cerevisiae Proteins
  • Cycloheximide
  • MET8 protein, S cerevisiae
  • Ferrochelatase