Molecular cloning and nucleotide sequences of cDNAS encoding subunits I, II, and IX of Euglena gracilis mitochondrial complex III

Jin Yan Cui, Kuniaki Mukai, Kazuhiko Saeki, Hiroshi Matsubara

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cDNA clones encoding subunits I, II, and IX of Euglena gracilis mitochondrial complex III have been isolated from a λgtll cDNA expression library by immunoscreening with an antiserum against the complex of the organism. Determination of the nucleotide sequences and amino-terminal amino acid sequences of purified subunits revealed that subunits II and IX, respectively, consist of 432 and 70 amino acids as their mature forms and possess potential presequences of 42 and 30 amino acids. The amino-terminal parts of the prese-quences had typical structural features of the mitochondrial targeting signal. Such features were also found at the amino-terminal region of the predicted subunit I protein, which comprises 494 residues. However, the amino terminus of the purified subunit I could not be detected, possibly because of a post-translational modification. Euglena subunits I and II both showed similarities to the members of the protein family which comprises complex III core proteins, mitochondrial processing peptidases (MPP) and processing enhancing proteins (PEP). Namely, the Euglena subunit I could be assigned to core 1 protein and the subunit II to core 2 protein in the family. In contrast, the subunit IX seemed to be peculiar to Euglena complex III. At 5'-untranslated regions, the three cloned cDNAs for subunits I, II, and IX had a common poly(T)CG structure which has also been reported for other Euglena cDNAs of nuclear genes.

Original languageEnglish
Pages (from-to)98-107
Number of pages10
JournalJournal of biochemistry
Issue number1
Publication statusPublished - 1994 Jan
Externally publishedYes



  • Complex
  • Cytochrome bc1
  • Euglena gracilis
  • Molecular evolution

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology

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