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Gene Review

COB  -  cytochrome b

Saccharomyces cerevisiae S288c

Synonyms: COB1, CYTB, Complex III subunit 3, Complex III subunit CYTB, Complex III subunit III, ...
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Disease relevance of COB


High impact information on COB

  • Complex III (CIII; ubiquinol cytochrome c reductase of the mitochondrial respiratory chain) catalyzes electron transfer from succinate and nicotinamide adenine dinucleotide-linked dehydrogenases to cytochrome c. CIII is made up of 11 subunits, of which all but one (cytochrome b) are encoded by nuclear DNA [6].
  • Group II intron bI1, the first intron of the COB gene in the mitochondria of S. cerevisiae, is able to self-splice in vitro with the basic pathway similar to nuclear pre-mRNA splicing [7].
  • bI4 maturase, encoded by the fourth intron of the yeast mitochondrial cytochrome b gene, controls the splicing of both the fourth intron of the cytochrome b gene and the fourth intron of the gene encoding subunit I of cytochrome oxidase [8].
  • Critical sequences within mitochondrial introns: cis-dominant mutations of the "cytochrome-b-like" intron of the oxidase gene [9].
  • We have established the DNA sequence of nine yeast mutants that prevent the expression either of the split cytochrome b gene alone (five mutants) or of two split genes, the cytochrome b gene and the cytochrome oxidase subunit I gene (four mutants) [10].

Chemical compound and disease context of COB


Biological context of COB

  • Transcripts of COXI and COB genes harboring multiple introns are degraded in the absence of PIM1 [11].
  • Upon induction of respiration, the steady-state level of the long transcripts decreases while that of the short transcripts increases reciprocally, an unexpected result since the product of the long transcripts is required for COB mRNA stability and thus for respiration [12].
  • Mutation of any nucleotide in the CCG causes the same phenotype as cbp1 mutations, i.e., destabilization of both COB precursor and mature message [13].
  • Hybridization experiments showed, that it is (i) a single copy gene, (ii) also present in strain D273-10B, containing the "short form" mitochondrial genome (lacking the COB introns bI1-bI3), and (iii) located on chromosome IX [14].
  • Cytochrome b is the only mitochondrially synthesized component of the respiratory chain complex III [15].

Anatomical context of COB


Associations of COB with chemical compounds


Physical interactions of COB

  • CBP1 is a yeast nuclear gene encoding a mitochondrial protein that stabilizes the 5' end of cytochrome b (cob) pre-mRNA [15].
  • Cbt1p is also required for stabilizing the mature cytochrome b mRNA after 5' processing [25].

Regulatory relationships of COB

  • The NAM1 nuclear gene was shown to control the stability and/or processing of mitochondrial transcripts of the cytochrome b, cytochrome oxidase subunit I and ATP synthase subunit VI genes [Groudinsky O., Bousquet I., Wallis M. G., Slonimski, P. P. & Dujardin G. (1993) Mol. Gen. Genet. 240, 419-427] [26].
  • Translation of mitochondrial cytochrome b mRNA in yeast is activated by the product of the nuclear gene CBS1 [27].
  • In Saccharomyces cerevisiae, the nuclear-encoded protein Cbp1 promotes stability and translation of mitochondrial cytochrome b transcripts through interaction with the 5' untranslated region [28].
  • Mutations in CBP3 are expressed in the absence of spectrally and immunologically detectable cytochrome b, a catalytic subunit of coenzyme QH2-cytochrome c reductase [29].
  • Based on this identification, Abc1p was postulated to activate the bc1 complex and function as a chaperone of cytochrome b [30].

Other interactions of COB

  • Premature 3'-end formation of CBP1 mRNA results in the downregulation of cytochrome b mRNA during the induction of respiration in Saccharomyces cerevisiae [12].
  • However, cytochrome b protein is not synthesized, and thus the Delta cbp1 Delta pet127 strain does not respire [31].
  • The ox1-79 strains exhibit a total absence of cytochrome aa3 and a decrease in cytochrome b, even in a strain devoid of mitochondrial introns, in which cox1 and cytb mRNAs normally accumulate [32].
  • Yeast nuclear gene CBS2, required for translational activation of cytochrome b, encodes a basic protein of 45 kDa [33].
  • 3. Mutations in COB 1 have been found to be linked to the OLI1 locus in some but not in other strains of S. cervisiae [16].

Analytical, diagnostic and therapeutic context of COB

  • Generation of temperature-sensitive cbp1 strains of Saccharomyces cerevisiae by PCR mutagenesis and in vivo recombination: characteristics of the mutant strains imply that CBP1 is involved in stabilization and processing of cytochrome b pre-mRNA [34].
  • Mutants D47G and D47N were respiratory deficient and analysis of complex components by immunoblotting and spectral analysis of cytochrome b suggests defective assembly [35].
  • In cbp1 mutant strains, cytochrome b gene (cob) transcripts are not detectable by Northern blot analysis [18].
  • This conclusion is based on the sequence analysis of mitochondrial DNA regions coding for structural genes of cytochrome b, cytochrome oxidase, and the ATPase [36].
  • Site-directed mutagenesis was also used to model selected regions of the mammalian Qo site in yeast cytochrome b in order to further understand the differential efficacy of these QoI in the mammalian and pathogen bc1 complexes [37].


  1. Electron-transfer restoration by vitamin K3 in a complex III-deficient mutant of S. cerevisiae and sequence of the corresponding cytochrome b mutation. Brivet-Chevillotte, P., di Rago, J.P. FEBS Lett. (1989) [Pubmed]
  2. Revealing the complementation of ferredoxin by cytochrome b (5) in the Spirulina- (6)-desaturation reaction by N-terminal fusion and co-expression of the fungal-cytochrome b (5) domain and Spirulina- (6)-acyl-lipid desaturase. Hongsthong, A., Subudhi, S., Sirijuntarut, M., Kurdrid, P., Cheevadhanarak, S., Tanticharoen, M. Appl. Microbiol. Biotechnol. (2006) [Pubmed]
  3. An inhibitor of mitochondrial respiration which binds to cytochrome b and displaces quinone from the iron-sulfur protein of the cytochrome bc1 complex. von Jagow, G., Ljungdahl, P.O., Graf, P., Ohnishi, T., Trumpower, B.L. J. Biol. Chem. (1984) [Pubmed]
  4. Characterization of mutations in the cytochrome b subunit of the bc1 complex of Rhodobacter sphaeroides that affect the quinone reductase site (Qc). Hacker, B., Barquera, B., Crofts, A.R., Gennis, R.B. Biochemistry (1993) [Pubmed]
  5. Aggregates of yeast mitochondrial cytochrome b observed after electrophoresis. Beattie, D.S., Clejan, L. J. Bioenerg. Biomembr. (1980) [Pubmed]
  6. A mutant mitochondrial respiratory chain assembly protein causes complex III deficiency in patients with tubulopathy, encephalopathy and liver failure. de Lonlay, P., Valnot, I., Barrientos, A., Gorbatyuk, M., Tzagoloff, A., Taanman, J.W., Benayoun, E., Chrétien, D., Kadhom, N., Lombès, A., de Baulny, H.O., Niaudet, P., Munnich, A., Rustin, P., Rötig, A. Nat. Genet. (2001) [Pubmed]
  7. Integration of group II intron bI1 into a foreign RNA by reversal of the self-splicing reaction in vitro. Mörl, M., Schmelzer, C. Cell (1990) [Pubmed]
  8. A mitochondrial RNA maturase gene transferred to the yeast nucleus can control mitochondrial mRNA splicing. Banroques, J., Delahodde, A., Jacq, C. Cell (1986) [Pubmed]
  9. Critical sequences within mitochondrial introns: cis-dominant mutations of the "cytochrome-b-like" intron of the oxidase gene. Netter, P., Jacq, C., Carignani, G., Slonimski, P.P. Cell (1982) [Pubmed]
  10. Critical sequences within mitochondrial introns: pleiotropic mRNA maturase and cis-dominant signals of the box intron controlling reductase and oxidase. De La Salle, H., Jacq, C., Slonimski, P.P. Cell (1982) [Pubmed]
  11. The ATP-dependent PIM1 protease is required for the expression of intron-containing genes in mitochondria. van Dyck, L., Neupert, W., Langer, T. Genes Dev. (1998) [Pubmed]
  12. Premature 3'-end formation of CBP1 mRNA results in the downregulation of cytochrome b mRNA during the induction of respiration in Saccharomyces cerevisiae. Sparks, K.A., Mayer, S.A., Dieckmann, C.L. Mol. Cell. Biol. (1997) [Pubmed]
  13. Suppressor analysis of mutations in the 5'-untranslated region of COB mRNA identifies components of general pathways for mitochondrial mRNA processing and decay in Saccharomyces cerevisiae. Chen, W., Islas-Osuna, M.A., Dieckmann, C.L. Genetics (1999) [Pubmed]
  14. Cloning of a nuclear gene MRS1 involved in the excision of a single group I intron (bI3) from the mitochondrial COB transcript in S. cerevisiae. Kreike, J., Schulze, M., Pillar, T., Körte, A., Rödel, G. Curr. Genet. (1986) [Pubmed]
  15. The yeast CBP1 gene produces two differentially regulated transcripts by alternative 3'-end formation. Mayer, S.A., Dieckmann, C.L. Mol. Cell. Biol. (1989) [Pubmed]
  16. Assembly of the mitochondrial membrane system. XVIII. Genetic loci on mitochondrial DNA involved in cytochrome b biosynthesis. Tzagoloff, A., Foury, F., Akai, A. Mol. Gen. Genet. (1976) [Pubmed]
  17. Saccharomyces cerevisiae translational activator Cbs1p is associated with translationally active mitochondrial ribosomes. Krause-Buchholz, U., Schöbel, K., Lauffer, S., Rödel, G. Biol. Chem. (2005) [Pubmed]
  18. CBP1 function is required for stability of a hybrid cob-oli1 transcript in yeast mitochondria. Mittelmeier, T.M., Dieckmann, C.L. Curr. Genet. (1990) [Pubmed]
  19. Subunit 9 of the Saccharomyces cerevisiae cytochrome bc1 complex is required for insertion of EPR-detectable iron-sulfur cluster into the Rieske iron-sulfur protein. Phillips, J.D., Graham, L.A., Trumpower, B.L. J. Biol. Chem. (1993) [Pubmed]
  20. Ubiquinol-cytochrome c oxidoreductase. The redox reactions of the bis-heme cytochrome b in ubiquinone-sufficient and ubiquinone-deficient systems. Matsuno-Yagi, A., Hatefi, Y. J. Biol. Chem. (1996) [Pubmed]
  21. Identification of multiple transcriptional initiation sites on the yeast mitochondrial genome by in vitro capping with guanylyltransferase. Christianson, T., Rabinowitz, M. J. Biol. Chem. (1983) [Pubmed]
  22. Evidence for ribosomes involved in splicing of yeast mitochondrial transcripts. Schmelzer, C., Schweyen, R.J. Nucleic Acids Res. (1982) [Pubmed]
  23. Failure to insert the iron-sulfur cluster into the Rieske iron-sulfur protein impairs both center N and center P of the cytochrome bc1 complex. Gutierrez-Cirlos, E.B., Merbitz-Zahradnik, T., Trumpower, B.L. J. Biol. Chem. (2002) [Pubmed]
  24. The preferential binding of dicyclohexylcarbodiimide to cytochrome b and phospholipids in soluble complex III from yeast mitochondria. Beattie, D.S., Clejan, L., Bosch, C.G. J. Biol. Chem. (1984) [Pubmed]
  25. CBT1 interacts genetically with CBP1 and the mitochondrially encoded cytochrome b gene and is required to stabilize the mature cytochrome b mRNA of Saccharomyces cerevisiae. Ellis, T.P., Schonauer, M.S., Dieckmann, C.L. Genetics (2005) [Pubmed]
  26. The NAM1 protein (NAM1p), which is selectively required for cox1, cytb and atp6 transcript processing/stabilisation, is located in the yeast mitochondrial matrix. Wallis, M.G., Groudinsky, O., Slonimski, P.P., Dujardin, G. Eur. J. Biochem. (1994) [Pubmed]
  27. In vitro and in vivo studies on the mitochondrial import of CBS1, a translational activator of cytochrome b in yeast. Körte, A., Forsbach, V., Gottenöf, T., Rödel, G. Mol. Gen. Genet. (1989) [Pubmed]
  28. The mitochondrial message-specific mRNA protectors Cbp1 and Pet309 are associated in a high-molecular weight complex. Krause, K., Lopes de Souza, R., Roberts, D.G., Dieckmann, C.L. Mol. Biol. Cell (2004) [Pubmed]
  29. Identification and characterization of a new gene (CBP3) required for the expression of yeast coenzyme QH2-cytochrome c reductase. Wu, M., Tzagoloff, A. J. Biol. Chem. (1989) [Pubmed]
  30. A tRNA(TRP) gene mediates the suppression of cbs2-223 previously attributed to ABC1/COQ8. Hsieh, E.J., Dinoso, J.B., Clarke, C.F. Biochem. Biophys. Res. Commun. (2004) [Pubmed]
  31. Cbp1 is required for translation of the mitochondrial cytochrome b mRNA of Saccharomyces cerevisiae. Islas-Osuna, M.A., Ellis, T.P., Marnell, L.L., Mittelmeier, T.M., Dieckmann, C.L. J. Biol. Chem. (2002) [Pubmed]
  32. OXA1, a Saccharomyces cerevisiae nuclear gene whose sequence is conserved from prokaryotes to eukaryotes controls cytochrome oxidase biogenesis. Bonnefoy, N., Chalvet, F., Hamel, P., Slonimski, P.P., Dujardin, G. J. Mol. Biol. (1994) [Pubmed]
  33. Yeast nuclear gene CBS2, required for translational activation of cytochrome b, encodes a basic protein of 45 kDa. Michaelis, U., Schlapp, T., Rödel, G. Mol. Gen. Genet. (1988) [Pubmed]
  34. Generation of temperature-sensitive cbp1 strains of Saccharomyces cerevisiae by PCR mutagenesis and in vivo recombination: characteristics of the mutant strains imply that CBP1 is involved in stabilization and processing of cytochrome b pre-mRNA. Staples, R.R., Dieckmann, C.L. Genetics (1993) [Pubmed]
  35. The functional role of conserved acidic residues of the Qcr7 protein of the cytochrome bc(1) complex in Saccharomyces cerevisiae. Lee, S.Y., Raha, S., Nagar, B., Robinson, B.H. Arch. Biochem. Biophys. (2001) [Pubmed]
  36. Use of the UGA terminator as a tryptophan codon in yeast mitochondria. Macino, G., Coruzzi, G., Nobrega, F.G., Li, M., Tzagoloff, A. Proc. Natl. Acad. Sci. U.S.A. (1979) [Pubmed]
  37. Re-examination of inhibitor resistance conferred by Qo-site mutations in cytochrome b using yeast as a model system. Fisher, N., Meunier, B. Pest Manag. Sci. (2005) [Pubmed]
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