title: Poly(A)-tail-promoted translation in yeast: implications for translational control.
abstract: The cap structure and the poly(A) tail synergistically activate mRNA translation in vivo. Recent work using Saccharomyces cerevisiae spheroplasts and a yeast cell-free translation system revealed that the poly(A) tail can function as an independent promotor for ribosome recruitment, to internal initiation sites within an mRNA. This raises the question of how regulatory upstream open reading frames and translational repressor proteins binding to the 5'UTR can function, as well as how regulated polyadenylation can support faithful activation of protein synthesis. We investigated the function of the regulatory upstream open reading frame 4 from the yeast GCN 4 gene and the effect of IRP-1 binding to an iron-responsive element introduced into the 5' UTR of reporter mRNAs. Both manipulations effectively block cap-dependent translation, whereas ribosome recruitment promoted by the poly(A) tail under non-competitive conditions can efficiently bypass both blocks. We show that the synergistic use of both, the cap structure and the poly-A tail enforced by mRNA competition reinstates the full extent of translational control by both types of 5' UTR regulatory elements. With a view towards regulated polyadenylation, we studied the function of poly(A) tails of defined length on the translation of capped mRNAs. We find that poly(A) tail elongation increases translational efficiency, particularly under competitive conditions. Our results integrate recent findings on the function of the poly(A) tail into an understanding of translational control.
authors.affiliation: Gene Expression Programme, European Molecular Biology Laboratory, Heidelberg, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Preiss
authors.forename: M
authors.initials: M
authors.lastname: Muckenthaler
authors.forename: M W
authors.initials: MW
authors.lastname: Hentze
mesh_terms: D020121:5' Untranslated Regions / Q000235:genetics; D001483:Base Sequence; D001667:Binding, Competitive; D015500:Chloramphenicol O-Acetyltransferase / Q000276:immunology; D004268:DNA-Binding Proteins; D005656:Fungal Proteins / Q000235:genetics; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal / Q000235:genetics*; D035941:Iron Regulatory Protein 1; D035925:Iron-Regulatory Proteins; D007506:Iron-Sulfur Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D008970:Molecular Weight; D016297:Mutagenesis, Site-Directed; D016366:Open Reading Frames / Q000235:genetics; D011233:Precipitin Tests; D014176:Protein Biosynthesis / Q000235:genetics*; D011494:Protein Kinases / Q000235:genetics; D012315:RNA Caps / Q000235:genetics; D012331:RNA, Fungal / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics* / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D013728:Terminator Regions, Genetic / Q000235:genetics*; D014158:Transcription, Genetic; D014529:Uridine
chemical_list: D020121:5' Untranslated Regions; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D035925:Iron-Regulatory Proteins; D007506:Iron-Sulfur Proteins; D012315:RNA Caps; D012331:RNA, Fungal; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D029701:Saccharomyces cerevisiae Proteins; D015500:Chloramphenicol O-Acetyltransferase; D011494:Protein Kinases; D035941:Iron Regulatory Protein 1; D014529:Uridine