The INA complex facilitates assembly of the peripheral stalk of the mitochondrial F 1 F o ‐ ATP synthase

Mitochondrial F 1 F o ‐ ATP synthase generates the bulk of cellular ATP . This molecular machine assembles from nuclear‐ and mitochondria‐encoded subunits. Whereas chaperones for formation of the matrix‐exposed hexameric F 1 ‐ ATP ase core domain have been identified, insight into how the nuclear‐encoded F 1 ‐domain assembles with the membrane‐embedded F o ‐region is lacking. Here we identified the INA complex ( INAC ) in the inner membrane of mitochondria as an assembly factor involved in this process. Ina22 and Ina17 are INAC constituents that physically associate with the F 1 ‐module and peripheral stalk, but not with the assembled F 1 F o ‐ ATP synthase. Our analyses show that loss of Ina22 and Ina17 specifically impairs formation of the peripheral stalk that connects the catalytic F 1 ‐module to the membrane embedded F o ‐domain. We conclude that INAC represents a matrix‐exposed inner membrane protein complex that facilitates peripheral stalk assembly and thus promotes a key step in the biogenesis of mitochondrial F 1 F o ‐ ATP synthase.