Tim44 is an essential component of the machinery that mediates the translocation of nuclear-encoded proteins across the mitochondrial inner membrane. Tim44 is thought to bind phospholipids of the mitochondrial inner membrane both by electrostatic interactions and by penetrating the polar head group region. This family includes the C-terminal region of Tim44 that has been shown to form a stable proteolytic fragment in yeast. This region is also found in a set of smaller bacterial proteins. The molecular function of the bacterial members of this family is unknown but transport seems likely. The crystal structure of the C terminal of Tim44 has revealed a large hydrophobic pocket which might play an important role in interacting with the acyl chains of lipid molecules in the mitochondrial membrane.