1. Chromosomes and Gene Expression
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Unfolded Protein Response: Silence without stress

  1. David J Young
  2. Nicholas R Guydosh  Is a corresponding author
  1. National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, United States
Cite this article as: eLife 2016;5:e22073 doi: 10.7554/eLife.22073
1 figure


A functional Hac1 protein is made only if a block that prevents the initiation of translation is removed.

(Left) The translation of two mRNA exons (shown here in blue and purple) results in the production of the Hac1 protein. However, unspliced HAC1 mRNA contains an intron (orange) that, in the absence of endoplasmic reticulum stress, undergoes base-pairing interactions with its own 5’UTR. These interactions prevent most 40S ribosomes (blue oval) from loading onto the mRNA and initiating translation. When the endoplasmic reticulum becomes stressed (middle panel), Ire1 proteins (black triangles) splice out the intron. The spliced HAC1 mRNA can then be translated to form the full-length Hac1 protein, which triggers the unfolded protein response in order to relieve endoplasmic reticulum stress. (Right) In the absence of stress, some 40S ribosomes (blue ovals) manage to bypass the base-pairing interactions. In this case, the second exon is not translated, and a new sequence is found at the C-terminal end of the protein (red). This "degron tag" is recognized by a protein adaptor called Duh1, which targets Hac1 for ubiquitination – a process that involves the formation of a complex that also includes E2, Cul1 and Skp1 proteins. This ubiquitination marks the protein for rapid degradation by the proteasome.

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