Mitochondrial protein that is likely to be responsible for thermogenic respiration. Likely to function in mitochondrial uncoupling i.e. creating mitochondrial proton leaks across the inner mitochondrial membrane and can therefore dissipate the mitochondrial proton gradient and convert the energy of substrate oxidation into heat instead of ATP. Involved in cold tolerance, it is required for development to the adult stage at low temperatures. RNAi-mediated knockdown is adult lethal at low temperatures. At 15 degrees Celsius there is a severe reduction in the number of larvae and flies do not survive to the adult stage. Second instar larvae moved from 23 to 14 degrees Celsius show no heat production in response to the decrease in temperature. In second instar larvae body wall preparations, maximal oxygen consumption rate (i.e. mitochondrial respiration) is significantly higher than the controls, and the addition of the uncoupler carbonyl cyanide p-[trifluoromethoxy]-phenyl-hydrazone followed by the ATP inhibitor oligomycin results in a threefold increase in the oxygen consumption rate. Uncoupling in larval mitochondria in response to the addition of palmitate is also suppressed. Belongs to the mitochondrial carrier (TC 2.A.29) family.