The mitochondrial proteins Ssq1 and Jac1 are required for the assembly of iron sulfur clusters in mitochondria

J Mol Biol. 2001 Mar 30;307(3):815-25. doi: 10.1006/jmbi.2001.4527.


Mitochondria of the yeast Saccharomyces cerevisiae contain three different Hsp70 chaperones, Ssc1, Ecm10 and Ssq1. Ssc1 is an essential protein that mediates the import of nuclear-encoded proteins into the organelle and their subsequent folding. The nucleotide state of Ssc1 is thereby regulated by the nucleotide exchange factor Mge1. Here, we show that Mge1 interacts with Ssq1 in an ATP-dependent manner, suggesting that Mge1 also regulates Ssq1 function. In contrast to Ssc1, Ssq1 does not associate with the Tim44 subunit of the protein translocating complex, indicating a different function of both chaperones. Mutants in Ssq1 were reported to have low levels of iron sulfur (FeS) cluster-containing enzymes. Employing an assay that allowed us to monitor the conversion of the apoform of mitochondrial ferredoxin into its FeS-containing holoform, Ssq1 was demonstrated to be required for the FeS cluster assembly in mitochondria. The mitochondrial DnaJ homolog Jac1 is crucial for this process, whereas Mdj1 function is dispensable. Furthermore, the presence of frataxin is necessary for FeS cluster assembly into ferredoxin suggesting a role for frataxin at the level of the formation of holo-ferredoxin.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphate / metabolism
  • Apoproteins / metabolism
  • Carrier Proteins / metabolism
  • Cell Division
  • Ferredoxins / chemistry
  • Ferredoxins / metabolism*
  • Fungal Proteins / genetics
  • Fungal Proteins / metabolism*
  • HSP70 Heat-Shock Proteins
  • Heat-Shock Proteins*
  • Iron-Binding Proteins*
  • Kinetics
  • Membrane Proteins / metabolism
  • Membrane Transport Proteins*
  • Mitochondria / metabolism*
  • Mitochondrial Membrane Transport Proteins*
  • Mitochondrial Proteins
  • Molecular Chaperones / genetics
  • Molecular Chaperones / metabolism*
  • Mutation / genetics
  • Phosphotransferases (Alcohol Group Acceptor) / genetics
  • Phosphotransferases (Alcohol Group Acceptor) / metabolism
  • Protein Binding
  • Protein Transport
  • Saccharomyces cerevisiae / cytology
  • Saccharomyces cerevisiae / enzymology
  • Saccharomyces cerevisiae / genetics
  • Saccharomyces cerevisiae / metabolism*
  • Saccharomyces cerevisiae Proteins*


  • Apoproteins
  • Carrier Proteins
  • Ferredoxins
  • Fungal Proteins
  • HSP70 Heat-Shock Proteins
  • Heat-Shock Proteins
  • Iron-Binding Proteins
  • JAC1 protein, S cerevisiae
  • MGE1 protein, S cerevisiae
  • Membrane Proteins
  • Membrane Transport Proteins
  • Mitochondrial Membrane Transport Proteins
  • Mitochondrial Proteins
  • Molecular Chaperones
  • SSQ1 protein, S cerevisiae
  • Saccharomyces cerevisiae Proteins
  • TIM44 protein, S cerevisiae
  • frataxin
  • Adenosine Triphosphate
  • Phosphotransferases (Alcohol Group Acceptor)