title: Evidence That Base-pairing Interaction between Intron and mRNA Leader Sequences Inhibits Initiation of HAC1 mRNA Translation in Yeast.
abstract: The Hac1 transcription factor in yeast up-regulates a collection of genes that control protein homeostasis. Base-pairing interactions between sequences in the intron and the 5'-untranslated region (5' UTR) of the HAC1 mRNA represses Hac1 protein production under basal conditions, whereas cytoplasmic splicing of the intron by the Ire1 kinase-endonuclease, activated under endoplasmic reticulum stress conditions, relieves the inhibition and enables Hac1 synthesis. Using a random mutational screen as well as site-directed mutagenesis, we identify point mutations within the 5' UTR-intron interaction site that derepress translation of the unspliced HAC1 mRNA. We also show that insertion of an in-frame AUG start codon upstream of the interaction site releases the translational block, demonstrating that an elongating ribosome can disrupt the interaction. Moreover, overexpression of translation initiation factor eIF4A, a helicase, enhances production of Hac1 from an mRNA containing an upstream AUG start codon at the beginning of the base-paired region. These results suggest that the major block of translation occurs at the initiation stage. Supporting this interpretation, the point mutations that enhanced Hac1 production resulted in an increased percentage of the HAC1 mRNA associating with polysomes versus free ribosomal subunits. Thus, our results provide evidence that the 5' UTR-intron interaction represses translation initiation on the unspliced HAC1 mRNA.
authors.affiliation: From the Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53211 and.
authors.forename: Leena
authors.initials: L
authors.lastname: Sathe
authors.affiliation: Eunice Kennedy Shriver NICHD, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: Cheryl
authors.initials: C
authors.lastname: Bolinger
authors.affiliation: From the Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53211 and.
authors.forename: M Amin-ul
authors.initials: MA
authors.lastname: Mannan
authors.affiliation: Eunice Kennedy Shriver NICHD, National Institutes of Health, Bethesda, Maryland 20892 tdever@nih.gov.
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Dever
authors.affiliation: From the Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53211 and deym@uwm.edu.
authors.forename: Madhusudan
authors.initials: M
authors.lastname: Dey
mesh_terms: D020121:5' Untranslated Regions / Q000235:genetics*; D020029:Base Pairing; D050976:Basic-Leucine Zipper Transcription Factors / Q000235:genetics* / Q000378:metabolism; D015152:Blotting, Northern; D015153:Blotting, Western; D018387:Codon, Initiator / Q000235:genetics; D039601:Eukaryotic Initiation Factor-4A / Q000235:genetics / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D007438:Introns / Q000235:genetics*; D016254:Mutagenesis, Insertional; D016297:Mutagenesis, Site-Directed; D017354:Point Mutation; D011132:Polyribosomes / Q000235:genetics / Q000378:metabolism; D014176:Protein Biosynthesis; D012326:RNA Splicing; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D020121:5' Untranslated Regions; D050976:Basic-Leucine Zipper Transcription Factors; D018387:Codon, Initiator; C091341:HAC1 protein, S cerevisiae; D012333:RNA, Messenger; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D039601:Eukaryotic Initiation Factor-4A
keywords: HAC1; endoplasmic reticulum stress (ER stress); eukaryotic initiation factor 4A (eIF4A); eukaryotic translation initiation; ribosome; translation; unfolded protein response (UPR)