This subfamily contains the MIX (Marker for type sIX effectors) IV clan (MIX IV) domain. MIX is a marker of type VI secretion system (T6SS) effectors carrying polymorphic C-terminal toxins. Predicted activity of the C-terminal toxin domains of Vibrionaceae MIX IV effectors is mainly pore-forming. Members of MIX IV are similar, in both sequence and synteny, to the Vibrio parahaemolyticus MIX-effector VP1388, but their activity is unknown. Notably, many toxins identified as T6SS effectors do not contain a recognizable delivery domain or signal, suggesting that additional delivery domains may exist.