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A more recent version of this article appeared on January 1, 2008
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Submitted on August 3, 2007
Revised on October 16, 2007
Accepted on November 1, 2007
Department of Biochemistry, University of Wisconsin-Madison, Madison, WI 53706
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 Hsp70 (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 (Pam18IMS) with Tim17, and the direct interaction of Pam18’s J-domain with Pam16’s J-like domain. 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 Pam16’s N-terminus 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.
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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