Bcl2-family proteins can have pro- or anti-apoptotic functions in different subcellular contexts. Jianjie Ma and colleagues are interested in how distinct tail-anchor domains of Bcl2 proteins relate to these pro- and anti-apoptotic effects and to localisation to specific organelles. On p. 2912 they investigate BFL1, a Bcl2 family member that is both pro- and anti-apoptotic and contains an unusual amphipathic tail domain. The researchers show that it is this tail – called ATAP (amphipathic tail-anchoring peptide) – that targets the protein to the mitochondrial membrane and, by inducing mutations in nucleotides flanking the ATAP sequence, they have defined the residues required for its localisation. They also show that ATAP is responsible for caspase-dependent apoptosis induced by BFL2 and identify the specific hydrophilic charged residues required for pro-apoptotic function. The researchers suggest that these residues compromise mitochondrial membrane permeability by forming a pore or interacting with mitochondrial proteins. Other peptides that cause mitochondria-mediated apoptosis are being tried as anti-cancer molecules; and the authors raise the possibility that ATAP peptides might also represent potential cancer therapies.