Plays a major role in programmed cell death (PCD, apoptosis) (PubMed:7907274, PubMed:10688797). egl-1 binds to and directly inhibits the activity of ced-9, releasing the cell death activator ced-4 from a ced-9/ced-4 containing protein complex and allowing ced-4 to activate the cell-killing caspase ced-3 (PubMed:9024666, PubMed:9027313, PubMed:9604928, PubMed:12894216, PubMed:15383288, PubMed:16208361). During larval development, required for the elimination of transient presynaptic components downstream of egl-1 and upstream of ced-4 and ced-3 apoptotic pathway (PubMed:26074078). Interacts with asymmetric homodimer ced-4; the interaction sequesters ced-4 (PubMed:9024666, PubMed:9027313, PubMed:15383288, PubMed:16208361). Interacts with egl-1; the interaction results in ced-4 release (PubMed:9604928, PubMed:12894216, PubMed:15383288). Interacts with dre-1; the interaction inhibits ced-9 activity, either directly or indirectly (PubMed:23431138). Interacts with dct-1 (PubMed:11114722). May form a complex composed of ced-9, ced-4 and mac-1 (PubMed:10101135). Intracellular membranes, mitochondrial, and perinuclear region (PubMed:9027313, PubMed:10688797). Localizes to synapses of DD motor neurons (PubMed:26074078). Synaptic localization is dependent on axonal mitochondria (PubMed:26074078). Abundant expression is seen in embryos and adults (PubMed:7907274). Expressed in embryos prior to elongation, at comma stage, at 1.5-fold stage and in adult gonad (PubMed:17021039). Belongs to the Bcl-2 family.