TOM71, A NOVEL HOMOLOG OF THE MITOCHONDRIAL PREPROTEIN RECEPTOR TOM70

The protein Tom71 is encoded by the open reading frame YHR117w (yeast chromosome VIII) and shares 53% amino acid sequence identity with Tom7 0, a protein import receptor of the mitochondrial outer membrane, We i nvestigated the cellular function of Tom71 and addressed the question of whether Tom71 and Tom70 fulfill similar functions, Like Tom70, Tom7 1 is anchored to the mitochondrial outer membrane via its N terminus, thereby exposing a large C-terminal domain to the cytosol, Tom71 is as sociated with the protein import complex of this membrane and can be c ross-linked to a protein with a molecular mass of 30-35 kDa, Disruptio n of the TOM71 gene does not reduce cell growth, except on nonfermenta ble carbon sources at elevated temperatures, Deletion of both the TOM7 1 and TOM70 genes does not acerbate this growth defect, In vitro impor t studies demonstrated no functional requirement for Tom71 in the impo rt of several preproteins destined for each of the mitochondrial subco mpartments, In particular, the import of Tom70-dependent preproteins i s minimally affected by the deletion of Tom71, irrespective of the pre sence or absence of the Tom70 receptor, Thus, despite their strikingly similar biochemical properties, Tom71 and Tom70 do not perform identi cal functions.