Incompletely synthesized polypeptides in the mitochondrial inner membrane are subject to rapid proteolysis. We demonstrate that Yta10p, a mitochondrial homologue of a conserved family of putative ATPases in Saccharomyces cerevisiae, is essential for this proteolytic process. Yta10p-dependent degradation requires divalent metal ions and the hydrolysis of ATP. Yta10p is an integral protein of the inner mitochondrial membrane exposing the carboxy terminus to the mitochondrial matrix space. Based on the presence of consensus binding sites for ATP, and for divalent metal ions found in a number of metal dependent endopeptidases, a direct role of Yta10p in the proteolytic breakdown of membrane-associated polypeptides in mitochondria is suggested.