Translational regulation via 5' mRNA leader sequences revealed by mutational analysis of the Arabidopsis translation initiation factor subunit eIF3h.
Eukaryotic translation initiation factor 3 (eIF3) consists of core subunits that are conserved from yeast to man as well as less conserved, noncore, subunits with potential regulatory roles. Whereas core subunits tend to be indispensable for cell growth, the roles of the noncore subunits remain poorly understood. We addressed the hypothesis that eIF3 noncore subunits have accessory functions that help to regulate translation initiation, by focusing on the Arabidopsis thaliana eIF3h subunit. Indeed, eIF3h was not essential for general protein translation. However, results from transient expression assays and polysome fractionation indicated that the translation efficiency of specific 5' mRNA leader sequences was compromised in an eif3h mutant, including the mRNA for the basic domain leucine zipper (bZip) transcription factor ATB2/AtbZip11, translation of which is regulated by sucrose. Among other pleiotropic developmental defects, the eif3h mutant required exogenous sugar to transit from seedling to vegetative development, but it was hypersensitive to elevated levels of exogenous sugars. The ATB2 mRNA was rendered sensitive to the eIF3h level by a series of upstream open reading frames. Moreover, eIF3h could physically interact with subunits of the COP9 signalosome, a protein complex implicated primarily in the regulation of protein ubiquitination, supporting a direct biochemical connection between translation initiation and protein turnover. Together, these data implicate eIF3 in mRNA-associated translation initiation events, such as scanning, start codon recognition, or reinitiation and suggest that poor translation initiation of specific mRNAs contributes to the pleiotropic spectrum of phenotypic defects in the eif3h mutant.
Kim
Tae-Houn
TH
Department of Botany, University of Tenessee, Knoxville, Tenessee 37996-1100, USA.
Kim
Byung-Hoon
BH
Yahalom
Avital
A
Chamovitz
Daniel A
DA
von Arnim
Albrecht G
AG
D020121:5' Untranslated Regions / Q000235:genetics*; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000096:biosynthesis / Q000235:genetics; D050976:Basic-Leucine Zipper Transcription Factors; D000075686:COP9 Signalosome Complex; D004252:DNA Mutational Analysis; D039621:Eukaryotic Initiation Factor-3 / Q000096:biosynthesis / Q000235:genetics*; D039642:Eukaryotic Initiation Factors / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000235:genetics*; D005816:Genetic Complementation Test; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes; D009154:Mutation / Q000235:genetics; D010447:Peptide Hydrolases; D014176:Protein Biosynthesis / Q000235:genetics*; D021122:Protein Subunits / Q000096:biosynthesis / Q000235:genetics; D011506:Proteins / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000235:genetics; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism
D020121:5' Untranslated Regions; C112599:ATB2 protein, Arabidopsis; D029681:Arabidopsis Proteins; D050976:Basic-Leucine Zipper Transcription Factors; D039621:Eukaryotic Initiation Factor-3; D039642:Eukaryotic Initiation Factors; D046912:Multiprotein Complexes; D021122:Protein Subunits; D011506:Proteins; D012333:RNA, Messenger; D014157:Transcription Factors; D025801:Ubiquitin; D010447:Peptide Hydrolases; D000075686:COP9 Signalosome Complex