Essential mediator of p53/TP53-dependent and p53/TP53-independent apoptosis (PubMed:11463391, PubMed:23340338). Promotes partial unfolding of BCL2L1 and dissociation of BCL2L1 from p53/TP53, releasing the bound p53/TP53 to induce apoptosis (PubMed:23340338). Regulates ER stress-induced neuronal apoptosis (By similarity).