BI-1 (Bax Inhibitor 1) is in anti-apoptotic protein that has been linked to protection from apoptosis induced endoplasmic reticulum (ER) stress (reviewed in Bailley-Maitre et al, 2007). BI-1 contains several transmembrane domains, localizes to ER membranes, and has cytoprotective functions that are conserved in both animals and plants. BI-1 suppresses apoptosis induced by ectopic expression of the proapoptotic protein Bax as well as other types of stimuli. Cells from BI-1 knockout (KO) mice are hypersensitivite to apoptosis induced by ER stress–causing chemical agents (thapsigargin, tunicamycin, and brefeldin A) or by ischemia-reperfusion (IR) injury. Conversely, overexpression of BI-1 protects against apoptosis induced by ER stress and IR. The mechanism by which BI-1 protects cells from ER-stress induced apoptosis remains to be fully elucidated, it is thought to involve regulation of Ca2+ handling by the ER.