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Cell. 1996 Nov 1;87(3):391-404.

A novel mechanism for regulating activity of a transcription factor that controls the unfolded protein response.

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Department of Biochemistry and Biophysics, University of California, School of Medicine, San Francisco 94143-0448, USA.


Cells respond to an accumulation of unfolded proteins in the endoplasmic reticulum (ER) by increasing transcription of genes encoding ER-resident proteins. The information is transmitted from the ER lumen to the nucleus by an intracellular signaling pathway, the unfolded protein response (UPR). We have identified a basic-leucine zipper transcription factor, Hac1p, that is required for the UPR and binds to the UPR element in the promoter of UPR-regulated genes. Surprisingly, Hac1p is found in UPR-activated cells only, and its level is controlled by regulated splicing of its mRNA. Splicing replaces the C-terminal tail of Hac1p with a different peptide that renders Hac1p more resistant to an otherwise extremely rapid ubiquitin-dependent degradation. We propose that the complex regulation of Hac1p expression serves to provide multiple levels at which the UPR can be controlled.

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