title: Activation of the Yeast UBI4 Polyubiquitin Gene by Zap1 Transcription Factor via an Intragenic Promoter Is Critical for Zinc-deficient Growth.
abstract: Stability of many proteins requires zinc. Zinc deficiency disrupts their folding, and the ubiquitin-proteasome system may help manage this stress. In Saccharomyces cerevisiae, UBI4 encodes five tandem ubiquitin monomers and is essential for growth in zinc-deficient conditions. Although UBI4 is only one of four ubiquitin-encoding genes in the genome, a dramatic decrease in ubiquitin was observed in zinc-deficient ubi4Δ cells. The three other ubiquitin genes were strongly repressed under these conditions, contributing to the decline in ubiquitin. In a screen for ubi4Δ suppressors, a hypomorphic allele of the RPT2 proteasome regulatory subunit gene (rpt2(E301K)) suppressed the ubi4Δ growth defect. The rpt2(E301K) mutation also increased ubiquitin accumulation in zinc-deficient cells, and by using a ubiquitin-independent proteasome substrate we found that proteasome activity was reduced. These results suggested that increased ubiquitin supply in suppressed ubi4Δ cells was a consequence of more efficient ubiquitin release and recycling during proteasome degradation. Degradation of a ubiquitin-dependent substrate was restored by the rpt2(E301K) mutation, indicating that ubiquitination is rate-limiting in this process. The UBI4 gene was induced ∼5-fold in low zinc and is regulated by the zinc-responsive Zap1 transcription factor. Surprisingly, Zap1 controls UBI4 by inducing transcription from an intragenic promoter, and the resulting truncated mRNA encodes only two of the five ubiquitin repeats. Expression of a short transcript alone complemented the ubi4Δ mutation, indicating that it is efficiently translated. Loss of Zap1-dependent UBI4 expression caused a growth defect in zinc-deficient conditions. Thus, the intragenic UBI4 promoter is critical to preventing ubiquitin deficiency in zinc-deficient cells.
authors.affiliation: From the Department of Nutritional Sciences, University of Wisconsin, Madison, Wisconsin 53706 and.
authors.forename: Colin W
authors.initials: CW
authors.lastname: MacDiarmid
authors.affiliation: From the Department of Nutritional Sciences, University of Wisconsin, Madison, Wisconsin 53706 and.
authors.forename: Janet
authors.initials: J
authors.lastname: Taggart
authors.affiliation: Department of Biology, Amherst College, Amherst, Massachusetts 01002.
authors.forename: Jeeyon
authors.initials: J
authors.lastname: Jeong
authors.affiliation: From the Department of Nutritional Sciences, University of Wisconsin, Madison, Wisconsin 53706 and.
authors.forename: Kittikhun
authors.initials: K
authors.lastname: Kerdsomboon
authors.affiliation: From the Department of Nutritional Sciences, University of Wisconsin, Madison, Wisconsin 53706 and eide@nutrisci.wisc.edu.
authors.forename: David J
authors.initials: DJ
authors.lastname: Eide
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal / Q000502:physiology*; D011401:Promoter Regions, Genetic / Q000502:physiology*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation / Q000502:physiology*; D025822:Ubiquitin C / Q000096:biosynthesis* / Q000235:genetics; D015032:Zinc / Q000378:metabolism*
chemical_list: D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; C417885:UBI4 protein, S cerevisiae; D025822:Ubiquitin C; C103264:ZAP1 protein, S cerevisiae; D000251:Adenosine Triphosphatases; C577243:Rpt2 protein, S cerevisiae; D015032:Zinc
keywords: gene transcription; proteasome; transcription promoter; ubiquitin; yeast; zinc