The TIM17 center dot 23 preprotein translocase of mitochondria: composition transport into the matrix

We have analysed the structural organization of the TIM17.23 complex, the p reprotein translocase of the mitochondrial inner membrane specific for prot ein targeting to the matrix. The components Tim17, Tim23 and Tim44 are pres ent in this complex in equimolar amounts. A sub-complex containing Tim23 an d Tim44 but no Tim17, or a sub-complex containing Tim23 and Tim17 but no Ti m44 was not detected. Tim44 is peripherally associated at the matrix side. Tim44 forms dimers which recruit two molecules of mt-Hsp70 to the sites of protein import. A sequential, hand-over-hand mode of interaction of these t wo mt-Hsp70 Tim44 complexes with a translocating polypeptide chain is propo sed.