Assembly of NADH: ubiquinone reductase (complex I) in Neurospora mitochondria. Independent pathways of nuclear-encoded and mitochondrially encoded subunits

J Mol Biol. 1990 Jun 20;213(4):845-57. doi: 10.1016/S0022-2836(05)80268-2.


NADH:ubiquinone reductase, the respiratory chain complex I of mitochondria, consists of some 25 nuclear-encoded and seven mitochondrially encoded subunits, and contains as redox groups one FMN, probably one internal ubiquinone and at least four iron-sulphur clusters. We are studying the assembly of the enzyme in Neurospora crassa. The flux of radioactivity in cells that were pulse-labelled with [35S]methionine was followed through immunoprecipitable assembly intermediates into the holoenzyme. Labelled polypeptides were observed to accumulate transiently in a Mr 350,000 intermediate complex. This complex contains all mitochondrially encoded subunits of the enzyme as well as subunits encoded in the nucleus that have no homologous counterparts in a small, merely nuclear-encoded form of the NADH:ubiquinone reductase made by Neurospora crassa cells poisoned with chloramphenicol. With regard to their subunit compositions, the assembly intermediate and small NADH:ubiquinone reductase complement each other almost perfectly to give the subunit composition of the large complex I. These results suggest that two pathways exist in the assembly of complex I that independently lead to the preassembly of two major parts, which subsequently join to form the complex. One preassembled part is related to the small form of NADH:ubiquinone reductase and contributes most of the nuclear-encoded subunits, FMN, three iron-sulphur clusters and the site for the internal ubiquinone. The other part is the assembly intermediate and contributes all mitochondrially encoded subunits, one iron-sulphur cluster and the catalytic site for the substrate ubiquinone. We discuss the results with regard to the evolution of the electron pathway through complex I.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Base Sequence
  • Cell Nucleus / enzymology*
  • Centrifugation, Density Gradient
  • Chromatography, High Pressure Liquid
  • DNA, Fungal / genetics
  • DNA, Mitochondrial / genetics
  • Genes, Fungal
  • Kinetics
  • Mitochondria / enzymology*
  • Molecular Sequence Data
  • Multienzyme Complexes / genetics
  • Multienzyme Complexes / metabolism*
  • NAD / metabolism*
  • NAD(P)H Dehydrogenase (Quinone)
  • Neurospora / enzymology*
  • Neurospora crassa / enzymology*
  • Precipitin Tests
  • Protein Biosynthesis
  • Quinone Reductases / genetics
  • Quinone Reductases / metabolism*


  • DNA, Fungal
  • DNA, Mitochondrial
  • Multienzyme Complexes
  • NAD
  • NAD(P)H Dehydrogenase (Quinone)
  • Quinone Reductases