title: The 39-kilodalton subunit of eukaryotic translation initiation factor 3 is essential for the complex's integrity and for cell viability in Saccharomyces cerevisiae.
abstract: Eukaryotic translation initiation factor 3 (eIF3) in the yeast Saccharomyces cerevisiae comprises about eight polypeptides and plays a central role in the binding of methionyl-tRNAi and mRNA to the 40S ribosomal subunit. The fourth largest subunit, eIF3-p39, was gel purified, and a 12-amino-acid tryptic peptide was sequenced, enabling the cloning of the TIF34 gene. TIF34 encodes a 38,753-Da protein that corresponds to eIF3-p39 in size and antigenicity. Disruption of TIF34 is lethal, and depletion of eIF3-p39 by glucose repression of TIF34 expressed from a GAL promoter results in cessation of cell growth. As eIF3-p39 levels fall, polysomes become smaller, indicating a role for eIF3-p39 in the initiation phase of protein synthesis. Unexpectedly, depletion results in degradation of all of the subunit proteins of eIF3 at a rate much faster than the normal turnover rates of these proteins. eIF3-p39 has 46% sequence identity with the p36 subunit of human eIF3. Both proteins are members of the WD-repeat family of proteins, possessing five to seven repeat elements. Taken together, the results indicate that eIF3-p39 plays an important, although not necessarily direct, role in the initiation phase of protein synthesis and suggest that it may be required for the assembly and maintenance of the eIF3 complex in eukaryotic cells.
authors.affiliation: Department of Biological Chemistry, School of Medicine, University of California, Davis 95616, USA.
authors.forename: T
authors.initials: T
authors.lastname: Naranda
authors.forename: M
authors.initials: M
authors.lastname: Kainuma
authors.forename: S E
authors.initials: SE
authors.lastname: MacMillan
authors.forename: J W
authors.initials: JW
authors.lastname: Hershey
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D039621:Eukaryotic Initiation Factor-3; D005656:Fungal Proteins / Q000032:analysis; D005800:Genes, Fungal / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D016366:Open Reading Frames / Q000235:genetics; D010446:Peptide Fragments; D010448:Peptide Initiation Factors / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology; D011132:Polyribosomes / Q000737:chemistry; D012331:RNA, Fungal / Q000032:analysis; D012333:RNA, Messenger / Q000032:analysis; D015183:Restriction Mapping; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology
chemical_list: D039621:Eukaryotic Initiation Factor-3; D005656:Fungal Proteins; D010446:Peptide Fragments; D010448:Peptide Initiation Factors; D012331:RNA, Fungal; D012333:RNA, Messenger; D029701:Saccharomyces cerevisiae Proteins; C102947:TIF34 protein, S cerevisiae; D014157:Transcription Factors