Overexpression of eIF4E in Saccharomyces cerevisiae causes slow growth and decreased alpha-factor response through alterations in CLN3 expression.
The association of G(1) cyclins and Cdc28/cyclin-dependent protein kinase catalyzes the cell cycle entry (Start) in budding yeast. Activation of Start is presumed to be triggered by a post-transcriptional increase in Cln3 during early G(1). Cells arrested by mating pheromone show a loss of cyclin-dependent protein kinase activity caused by transcriptional shutoff of cyclins and/or inhibition by Far1. We report that overexpression of eIF4E (Cdc33), a rate-limiting translation initiation factor, causes an increase in CLN3 mRNA translation, which results in increased expression of CLN2 and in slow growth and decreased alpha-factor response. This phenotype was abrogated in a Deltacln3 or Deltacln2 background. We isolated the transcription factor MBP1 as a multicopy suppressor of the growth and alpha-factor response defects. Furthermore, elevated MBP1, a transcriptional regulator of cyclins, altered the transcriptional start site in CLN3 mRNA, shifting it 45 nucleotides upstream of the normal. This lengthened 5'-untranslated region likely reduces translation efficiency and down-regulates CLN3 protein synthesis, thereby correcting for the excess translation promoted by elevated Cdc33. In addition, the CLN2 mRNA level returned to normal. We propose that regulation of translation initiation by Cdc33 plays a pivotal role in the activation of Start and cell cycle progression in budding yeast.
Anthony
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Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, 1501 Kings Highway, Shreveport, LA 71130-3932, USA.
Zong
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De Benedetti
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D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000378:metabolism*; D016213:Cyclins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D039561:Eukaryotic Initiation Factor-4E; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D000072235:Mating Factor; D010448:Peptide Initiation Factors / Q000378:metabolism*; D010455:Peptides / Q000494:pharmacology*; D010641:Phenotype; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000254:growth & development; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors / Q000378:metabolism; D024363:Transcription Initiation Site
C082721:CLN2 protein, S cerevisiae; C079895:CLN3 protein, S cerevisiae; D018797:Cell Cycle Proteins; D016213:Cyclins; D039561:Eukaryotic Initiation Factor-4E; D005656:Fungal Proteins; C083209:MBP1 protein, S cerevisiae; D010448:Peptide Initiation Factors; D010455:Peptides; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D000072235:Mating Factor