Protein involved in apoptosis; contains  BCL-2 homology (BH3) domain, member of BAX inhibitor family; reported to promote apoptosis under some conditions and to inhibit it in others; localizes to ER and vacuole; mediates a ubiquitin-related mitophagy pathway in both yeast and mammalian cells through association with Hsp70; translocates to mitochondria under apoptosis-inducing conditions in a process involving Mir1p and Cor1p