Component of the mitochondrial inner membrane i-AAA protease supercomplex, which degrades misfolded mitochondrial proteins. Together with MGR1, functions in an adapter complex that targets substrates to the i-AAA protease for degradation. Required for growth of cells lacking the mitochondrial genome. Component of the mitochondrial inner membrane i-AAA protease supercomplex composed of MGR1, MGR3 and YME1. With MGR1, forms a subcomplex that binds to YME1 and to substrates to facilitate proteolysis. Reduces proteolysis by YME1. Present with 8970 molecules/cell in log phase SD medium. Belongs to the MGR3 family.