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Vol. 19, Issue 1, 424-432, January 2008

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Interaction of the J-Protein Heterodimer Pam18/Pam16 of the Mitochondrial Import Motor with the Translocon of the Inner Membrane

Patrick R. D'Silva^*,, Brenda Schilke^*, Masaya Hayashi, and Elizabeth A. Craig

Department of Biochemistry, University of Wisconsin, Madison, Madison, WI 53706

Submitted August 3, 2007; Revised October 16, 2007; Accepted November 1, 2007
Monitoring Editor: Jeffrey Brodsky

Import of proteins across the inner mitochondrial membrane through the Tim23:Tim17 translocase requires the function of an essential import motor having mitochondrial 70-kDa heat-shock protein (mtHsp70) at its core. The heterodimer composed of Pam18, the J-protein partner of mtHsp70, and the related protein Pam16 is a critical component of this motor. We report that three interactions contribute to association of the heterodimer with the translocon: the N terminus of Pam16 with the matrix side of the translocon, the inner membrane space domain of Pam18 (Pam18_IMS) with Tim17, and the direct interaction of the J-domain of Pam18 with the J-like domain of Pam16. Pam16 plays a major role in translocon association, as alterations affecting the stability of the Pam18:Pam16 heterodimer dramatically affect association of Pam18, but not Pam16, with the translocon. Suppressors of the growth defects caused by alterations in the N terminus of Pam16 were isolated and found to be due to mutations in a short segment of TIM44, the gene encoding the peripheral membrane protein that tethers mtHsp70 to the translocon. These data suggest a model in which Tim44 serves as a scaffold for precise positioning of mtHsp70 and its cochaperone Pam18 at the translocon.

* These authors contributed equally to this work.

Present address: Department of Biochemistry, Indian Institute of Science, Bangalore, 560012, India.

Address correspondence to: Elizabeth A. Craig (ecraig{at}wisc.edu)

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