The import motor of the yeast mitochondrial TIM23 preprotein translocase contains two different J proteins, Tim14 and Mdj2

J Biol Chem. 2005 Sep 9;280(36):31608-14. doi: 10.1074/jbc.M502397200. Epub 2005 Jul 18.


The import motor of the mitochondrial (mt)TIM23 complex drives translocation of presequence-containing preproteins across the mitochondrial inner membrane in an ATP-dependent manner. Tim44 is the central component of the motor. It recruits mtHsp70, which binds the incoming preproteins. The J protein Tim14 stimulates the ATPase activity of mtHsp70 and thereby enables efficient binding of mtHsp70 to preproteins. Tim16 is a J-like protein that forms a stable subcomplex with Tim14 and recruits it to the translocase. All subunits of the TIM23 translocase but one are essential for yeast cell viability. Yeast cells contain a close homologue of Tim14, Mdj2. In contrast to Tim14, its deletion leads to no obvious growth defect. In the present study we analyzed Mdj2 and compared it with Tim14. Mdj2 forms a complex with Tim16 and is recruited to the TIM23 translocase. It stimulates the ATPase activity of mtHsp70 to the same extent that Tim14 does. Mdj2 is expressed at a lower level compared with Tim14, and its complex with Tim16 is less stable. However, overexpressed Mdj2 fully restores the growth of cells lacking Tim14. We conclude that Mdj2 is a functional J protein and a component of the mitochondrial import motor.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphatases / metabolism
  • Adenosine Triphosphate / metabolism
  • Amino Acid Sequence
  • Enzyme Precursors / physiology*
  • HSP70 Heat-Shock Proteins / metabolism
  • Membrane Proteins / genetics
  • Membrane Proteins / physiology*
  • Membrane Transport Proteins / genetics
  • Membrane Transport Proteins / metabolism
  • Membrane Transport Proteins / physiology*
  • Mitochondria / physiology*
  • Mitochondrial Membrane Transport Proteins
  • Molecular Sequence Data
  • Protein Transport / physiology
  • Saccharomyces cerevisiae / physiology
  • Saccharomyces cerevisiae Proteins / genetics
  • Saccharomyces cerevisiae Proteins / metabolism
  • Saccharomyces cerevisiae Proteins / physiology*
  • Sequence Alignment


  • Enzyme Precursors
  • HSP70 Heat-Shock Proteins
  • MDJ2 protein, S cerevisiae
  • Membrane Proteins
  • Membrane Transport Proteins
  • Mitochondrial Membrane Transport Proteins
  • Pam16 protein, S cerevisiae
  • Saccharomyces cerevisiae Proteins
  • TIM23 protein, S cerevisiae
  • Tim14 protein, S cerevisiae
  • Adenosine Triphosphate
  • Adenosine Triphosphatases