IRE-1 really has two faces," Dr. Blackwell says. "On the one hand, it senses misfolded proteins inside the ER, and it turns on a corrective mechanism called the unfolded protein response (UPR). On the other hand, when IRE-1 gets a signal from ROS molecules outside the ER, it shuts off the UPR response and turns on an antioxidant response. Also surprisingly, this functional switch is mediated by a single oxygen molecule, which attaches to a single amino acid at a very critical place in IRE-1 -- and this relatively subtle alteration has a dramatic effect."