Enables cytochrome-c oxidase activity. Acts upstream of or within several processes, including heart contraction; spinal cord motor neuron differentiation; and swimming behavior. Predicted to be located in mitochondrial inner membrane. Predicted to be active in mitochondrion. Human ortholog(s) of this gene implicated in Charcot-Marie-Tooth disease type 4K; Leigh disease; and mitochondrial complex IV deficiency nuclear type 1. Orthologous to human SURF1 (SURF1 cytochrome c oxidase assembly factor).