Catalytic subunit of the mitochondrial inner membrane i-AAA protease supercomplex required for mitochondrial inner membrane protein turnover. The protease is probably ATP-dependent. Important to maintain the integrity of the mitochondrial compartment. Required both for the degradation of unassembled subunit 2 of cytochrome c oxidase (COX2) and for efficient assembly of mitochondrial respiratory chain. Binds unfolded substrates in an ATPase-independent manner; binding of folded COX2, a physiological substrate, requires an active ATPase but when COX2 is destabilized an active ATPase is no longer necessary. Binds 1 zinc ion per subunit. Component of the mitochondrial inner membrane i-AAA protease supercomplex composed of MGR1, MGR3 and YME1. Interacts directly with MGR1. Although this protein does not have any predicted transmembrane helices it behaves like an integral membrane protein. An increased rate of escape of mtDNA to the nucleus, no growth on nonfermentable carbon sources at 37 degrees Celsius, a cold-sensitive defect in growth on fermentable carbon sources, lethality in rho- (cytoplasmic petite) cells. Present with 20100 molecules/cell in log phase SD medium. In the N-terminal section; belongs to the AAA ATPase family. In the C-terminal section; belongs to the peptidase M41 family.