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Biology Articles » Biochemistry » Signaling the Unfolded Protein Response from the Endoplasmic Reticulum » Figures

Figures
- Signaling the Unfolded Protein Response from the Endoplasmic Reticulum

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FIG. 1. Depiction of three UPR transducers and one master regulator. The domain structures of IRE1, PERK, and ATF6 and their associations with BiP are shown.

Figure 1

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FIG. 2. UPR signaling mediated by IRE1 and ATF6. Upon accumulation of unfolded protein in the ER lumen, BiP release from IRE1 permits dimerization to activate its kinase and RNase activities to initiate XBP1 mRNA splicing. Spliced XBP1 mRNA encodes a potent transcription factor that binds to the UPRE or ERSE sequence of many UPR target genes. Paradoxically, BiP release from ATF6 permits ATF6 transport to the Golgi compartment where full-length ATF6 (90 kDa) is cleaved by S1P and S2P proteases to yield a cytosolic fragment (50 kDa) that migrates to the nucleus to activate transcription of UPR-responsive genes. U-Pr, unfolded protein.

Figure 2

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FIG. 3. UPR signaling mediated by PERK. On accumulation of unfolded protein in the ER lumen, PERK is released from BiP, thus permitting its dimerization and activation. Activated PERK phosphorylates eIF2{alpha} to reduce the frequency of the mRNA translation initiation in general. However, selective mRNAs, such as GCN4 or ATF4 mRNA, can be preferentially translated by the phosphorylated eIF2{alpha}. U-Pr, unfolded protein.

Figure 3

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Source: J. Biol. Chem., Vol. 279, Issue 25, 25935-25938, June 18, 2004


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