Mutational analysis of the mitochondrial Rieske iron-sulfur protein of Saccharomyces cerevisiae. III. Import, protease processing, and assembly into the cytochrome bc1 complex of iron-sulfur protein lacking the iron-sulfur cluster

J Biol Chem. 1991 Nov 25;266(33):22485-92.


We have used site-directed mutagenesis of the Saccharomyces cerevisiae Rieske iron-sulfur protein gene (RIP 1) to convert cysteines 159, 164, 178, and 180 to serines, and to convert histidines 161 and 181 to arginines. These 4 cysteines and 2 histidines are conserved in all Rieske proteins sequenced to date, and 4 of these 6 residues are thought to ligate the iron-sulfur cluster to the apoprotein. We have also converted histidine 184 to arginine. This histidine is conserved only in respiring organisms. The site-directed mutations of the six fully conserved putative iron-sulfur cluster ligands result in an inactive iron-sulfur protein, lacking iron-sulfur cluster, and failure of the yeast to grow on nonfermentable carbon sources. In contrast, when histidine 184 is replaced by arginine, the iron-sulfur cluster is assembled properly and the yeast grow on nonfermentable carbon sources. The site-directed mutations of the 6 fully conserved residues do not prevent post-translational import of iron-sulfur protein precursor into mitochondria, nor do the mutations prevent processing of iron-sulfur protein precursor to mature size protein by mitochondrial proteases. Optical spectra of mitochondria from the six mutants indicate that cytochrome b is normal, in contrast to the deranged spectrum of cytochrome b which results when the iron-sulfur protein gene is deleted. In addition, mature size iron-sulfur apoprotein is associated with cytochrome bc1 complex purified from a site-directed mutant in which iron-sulfur cluster is not inserted. These results indicate that mature size iron-sulfur apoprotein, lacking iron-sulfur cluster, is inserted into the cytochrome bc1 complex, where it interacts with and preserves the optical properties of cytochrome b. Insertion of the iron-sulfur cluster is not an obligatory prerequisite to processing of the protein to its final size. Either the processing protease cannot distinguish between iron-sulfur protein with or without the iron-sulfur cluster, or insertion of the iron-sulfur cluster occurs after the protein is processed to its mature size, possibly after it is assembled in the cytochrome bc1 complex.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Base Sequence
  • Blotting, Western
  • Chromosome Deletion
  • Cytochromes / metabolism
  • Electron Spin Resonance Spectroscopy
  • Electron Transport Complex III / genetics*
  • Electron Transport Complex III / metabolism
  • Humans
  • Immunoblotting
  • Intracellular Membranes / enzymology
  • Iron-Sulfur Proteins / genetics*
  • Iron-Sulfur Proteins / metabolism
  • Mitochondria / metabolism*
  • Models, Structural
  • Molecular Sequence Data
  • Molecular Weight
  • Mutagenesis, Site-Directed*
  • Oligodeoxyribonucleotides
  • Plasmids
  • Protein Conformation
  • Restriction Mapping
  • Saccharomyces cerevisiae / genetics*
  • Saccharomyces cerevisiae / metabolism
  • Sequence Homology, Nucleic Acid
  • Submitochondrial Particles / enzymology


  • Cytochromes
  • Iron-Sulfur Proteins
  • Oligodeoxyribonucleotides
  • Rieske iron-sulfur protein
  • Electron Transport Complex III