(1 MISFOLDED PROTEINS IN ER SIGNAL nuclear NUCLEUS THE NEED FOR MORE ER CHAPERONES BY ACTIVATING A TRANSMEMBRANE chaperone mRNA KINASE 2 ACTIVATED KINASE TURNS INTO AN ENDORIBONUCLEASE CYTOSOL gene regulatory 3 ENDORIBONUCLEASE CUTS SPECIFIC protein RNA MOLECULES AT TWO POSITIONS. ER chaperone REMOVING AN INTRON 8曾 4 TWO EXONS ARE LIGATED TO mRNA匚 FORM AN ACTIVE mRNA exon exon e 5 mRNA IS TRANSLATED TO MAKE A GENE REGULATORY PROTEIN pre-mRNA (6 GENE REGULATORY PROTEIN ENTERS protein kinase (sensor) NUCLEUS AND ACTIVATES GENES ENCODING ER CHAPERONES ribonuclease ⊙ domain 7 CHAPERONES ARE MADE IN ER. WHERE THEY HELP FOLD PROTEINS misfolded protein ER LUMEN Figure 12-56 The unfolded protein response in yeast. By this intracellular signaling pathway, the accumulation of misfolded proteins the ER lumen signals to the nucleus to activate the transcription of that encode proteins that help the cell to cope with the abundance misfolded proteins in the ER