The mitochondrial Hsp70 controls the assembly of the F 1 F O -ATP synthase.

The mitochondrial F 1 F O -ATP synthase produces the bulk of cellular ATP. The soluble F 1 domain contains the catalytic head that is linked via the central stalk and the peripheral stalk to the membrane embedded rotor of the F O domain. The assembly of the F 1 domain and its linkage to the peripheral stalk is poorly understood. Here we show a dual function of the mitochondrial Hsp70 (mtHsp70) in the formation of the ATP synthase. First, it cooperates with the assembly factors Atp11 and Atp12 to form the F 1 domain of the ATP synthase. Second, the chaperone transfers Atp5 into the assembly line to link the catalytic head with the peripheral stalk. Inactivation of mtHsp70 leads to integration of assembly-defective Atp5 variants into the mature complex, reflecting a quality control function of the chaperone. Thus, mtHsp70 acts as an assembly and quality control factor in the biogenesis of the F 1 F O -ATP synthase.