How do we know this? Measuring ER stress

HAC1p (yeast), XBP1s (mammals) and bZIP60 (plant) proteins are all transactivators: once expressed from spliced mRNA, they enter the nucleus and stimulate expression of UPR genes. Responses: Increased ERAD (ER-associated protein degradation) Increased chaperone production (improved protein folding) Increased protein trafficking rates (clearing misfolded proteins from the ER, particularly in yeast)