COB/Q0105 Summary Help

Standard Name COB
Systematic Name Q0105
Alias COB1 , CYTB
Feature Type ORF, Verified
Description Cytochrome b; mitochondrially encoded subunit of the ubiquinol-cytochrome c reductase complex which includes Cobp, Rip1p, Cyt1p, Cor1p, Qcr2p, Qcr6p, Qcr7p, Qcr8p, Qcr9p, and Qcr10p (1, 2 and see Summary Paragraph)
Name Description CytochrOme B
Chromosomal Location
ChrMito:36540 to 43647 | ORF Map | GBrowse
Gene Ontology Annotations All COB GO evidence and references
  View Computational GO annotations for COB
Molecular Function
Manually curated
Biological Process
Manually curated
Cellular Component
Manually curated
Classical genetics
gain of function
reduction of function
28 total interaction(s) for 25 unique genes/features.
Physical Interactions
  • Affinity Capture-MS: 3
  • Affinity Capture-Western: 9
  • Co-fractionation: 7
  • Protein-RNA: 1

Genetic Interactions
  • Dosage Rescue: 5
  • Synthetic Rescue: 3

Expression Summary
Length (a.a.) 385
Molecular Weight (Da) 43,656
Isoelectric Point (pI) 9.24
Phosphorylation PhosphoGRID | PhosphoPep Database
sequence information
ChrMito:36540 to 43647 | ORF Map | GBrowse
This feature contains embedded feature(s): BI2 | BI3 | BI4
Last Update Coordinates: 2000-05-19 | Sequence: 2000-05-19
Subfeature details
Most Recent Updates
Coordinates Sequence
CDS 1..415 36540..36954 2000-05-19 2000-05-19
Intron 416..1183 36955..37722 2000-05-19 2000-05-19
CDS 1184..1197 37723..37736 2000-05-19 2000-05-19
Intron 1198..2601 37737..39140 2000-05-19 2000-05-19
CDS 2602..2678 39141..39217 2000-05-19 2000-05-19
Intron 2679..4301 39218..40840 2000-05-19 2000-05-19
CDS 4302..4551 40841..41090 2000-05-19 2000-05-19
Intron 4552..5968 41091..42507 2000-05-19 2000-05-19
CDS 5969..6019 42508..42558 2000-05-19 2000-05-19
Intron 6020..6757 42559..43296 2000-05-19 2000-05-19
CDS 6758..7108 43297..43647 2000-05-19 2000-05-19
Retrieve sequences
Analyze Sequence
S288C only
S288C vs. other species
S288C vs. other strains
External Links All Associated Seq | Entrez Gene | Entrez RefSeq Protein | MIPS | Search all NCBI (Entrez) | UniProtKB
Primary SGDIDS000007270

The cytochrome bc1 complex (also known as ubiquinol:cytochrome c oxidoreductase, ubiquinol:ferricytochrome c oxidoreductase, and respiratory complex III) is a highly conserved enzyme of the mitochondrial respiratory chain (reviewed in 3). In S. cerevisiae it consists of three catalytic subunits, Cobp, Rip1p, and Cyt1p, plus seven additional subunits: Cor1p, Qcr2p, Qcr6p, Qcr7p, Qcr8p, Qcr9p, and Qcr10p (3, 4). The crystal structure of the complex shows that two functional units, each containing these ten subunits, associate with each other in the mitochondrial inner membrane (1). Assembly of a functional complex requires two proteins, Cbp3p and Cbp4p, that are not components of the complex but may associate with it during assembly (5). It also requires Bcs1p, an AAA-family ATPase that interacts with a precursor of the complex to mediate incorporation of the Rip1p and Qcr10p subunits (6). The mechanism of energy transfer by the complex, known as the protonmotive Q cycle, has been studied in detail (reviewed in 3). The net result of the Q cycle is the stepwise transfer of an electron through the complex from ubiquinol to cytochrome c (Cyc1p), coupled with the translocation of a proton across the mitochondrial inner membrane (3). The function of the cytochrome bc1 complex is essential to the energy-generating process of oxidative phosphorylation, which is carried out by the enzyme complexes of the mitochondrial respiratory chain. Cytochrome b (Cobp), which contains two b-type heme groups (3), is one of the catalytic subunits of the cytochrome bc1 complex and comprises a major part of the site at which ubiquinol is oxidized, termed center P of the enzyme (7).

Cytochrome b, encoded by the mitochondrial COB gene (8, 9, 2), is the only mitochondrially-encoded subunit of the cytochrome bc1 complex. The structure and expression of the COB gene are extremely complex: it contains multiple introns, whose number varies between strains (reviewed in 10), and its mRNA maturation and translation require multiple nuclear-encoded proteins. Generation of the correct 5' end of the COB mRNA, which is cotranscribed with an upstream tRNA gene, requires the action of Cbp1p and Cbt1p (11). The COB gene of the genome reference strain S288C has five introns, named bI1 through bI5 (12). The first intron, bI1, is a group II, self-splicing intron; the other introns are group I. The second through fourth introns (bI2, bI3, and bI4) contain open reading frames that are contiguous with the upstream COB exons, such that translation of alternately spliced mRNAs produces fusion proteins comprised of both cytochrome b sequences and intron-encoded sequences. These proteins have maturase activity and are involved in splicing of introns from both the COB and COX1 genes (13, 14, 15, 10). Splicing of the fifth intron, bI5, requires the nuclear-encoded protein Cbp2p (16). Translation of mRNAs bearing the COB 5'-untranslated leader requires the specific translational activators Cbs1p and Cbs2p (17).

Cytochrome b is highly conserved across bacteria and all eukaryotes (18). Mutations of the human ortholog MTCYB (OMIM) cause a variety of disease syndromes due to complex III deficiency (19, 20). Mutations conveying resistance to the anti-malarial and antifungal drug atovaquone are known to arise in the cytochrome b orthologs of parasites and fungi such as Plasmodium falciparum, Toxoplasma gondii, and Pneumocystis jirovecii (21, 22).

Last updated: 2007-05-29 Contact SGD

References cited on this page View Complete Literature Guide for COB
1) Hunte C, et al.  (2000) Structure at 2.3 A resolution of the cytochrome bc(1) complex from the yeast Saccharomyces cerevisiae co-crystallized with an antibody Fv fragment. Structure 8(6):669-84
2) Kreike J, et al.  (1979) The identification of apocytochrome b as a mitochondrial gene product and immunological evidence for altered apocytochrome b in yeast strains having mutations in the COB region of mitochondrial DNA. Eur J Biochem 101(2):607-17
3) Hunte C, et al.  (2003) Protonmotive pathways and mechanisms in the cytochrome bc1 complex. FEBS Lett 545(1):39-46
4) Brandt U, et al.  (1994) Isolation and characterization of QCR10, the nuclear gene encoding the 8.5-kDa subunit 10 of the Saccharomyces cerevisiae cytochrome bc1 complex. J Biol Chem 269(17):12947-53
5) Kronekova Z and Rodel G  (2005) Organization of assembly factors Cbp3p and Cbp4p and their effect on bc(1) complex assembly in Saccharomyces cerevisiae. Curr Genet 47(4):203-12
6) Cruciat CM, et al.  (1999) Bcs1p, an AAA-family member, is a chaperone for the assembly of the cytochrome bc(1) complex. EMBO J 18(19):5226-33
7) Wenz T, et al.  (2007) Mutational analysis of cytochrome b at the ubiquinol oxidation site of yeast complex III. J Biol Chem 282(6):3977-88
8) Tzagoloff A, et al.  (1976) Assembly of the mitochondrial membrane system. XVIII. Genetic loci on mitochondrial DNA involved in cytochrome b biosynthesis. Mol Gen Genet 149(1):33-42
9) Haid A, et al.  (1979) The mitochondrial COB region in yeast codes for apocytochrome b and is mosaic. Eur J Biochem 94(2):451-64
10) Pel HJ and Grivell LA  (1993) The biology of yeast mitochondrial introns. Mol Biol Rep 18(1):1-13
11) Ellis T, et al.  (2005) 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. Genetics 171(3):949-57
12) Foury F, et al.  (1998) The complete sequence of the mitochondrial genome of Saccharomyces cerevisiae. FEBS Lett 440(3):325-31
13) Lazowska J, et al.  (1980) Sequence of introns and flanking exons in wild-type and box3 mutants of cytochrome b reveals an interlaced splicing protein coded by an intron. Cell 22(2 Pt 2):333-48
14) De La Salle H, et al.  (1982) Critical sequences within mitochondrial introns: pleiotropic mRNA maturase and cis-dominant signals of the box intron controlling reductase and oxidase. Cell 28(4):721-32
15) Jacq C, et al.  (1984) Antibodies against a fused 'lacZ-yeast mitochondrial intron' gene product allow identification of the mRNA maturase encoded by the fourth intron of the yeast cob-box gene. EMBO J 3(7):1567-72
16) Tirupati HK, et al.  (1999) An RNA binding motif in the Cbp2 protein required for protein-stimulated RNA catalysis. J Biol Chem 274(43):30393-401
17) Rodel G  (1986) Two yeast nuclear genes, CBS1 and CBS2, are required for translation of mitochondrial transcripts bearing the 5'-untranslated COB leader. Curr Genet 11(1):41-5
18) Trumpower BL  (1990) Cytochrome bc1 complexes of microorganisms. Microbiol Rev 54(2):101-29
19) Blakely EL, et al.  (2005) A mitochondrial cytochrome b mutation causing severe respiratory chain enzyme deficiency in humans and yeast. FEBS J 272(14):3583-92
20) Fisher N and Meunier B  (2001) Effects of mutations in mitochondrial cytochrome b in yeast and man. Deficiency, compensation and disease. Eur J Biochem 268(5):1155-62
21) Kessl JJ, et al.  (2004) Molecular basis for atovaquone resistance in Pneumocystis jirovecii modeled in the cytochrome bc(1) complex of Saccharomyces cerevisiae. J Biol Chem 279(4):2817-24
22) Kessl JJ, et al.  (2006) Molecular basis of Toxoplasma gondii atovaquone resistance modeled in Saccharomyces cerevisiae. Mol Biochem Parasitol 146(2):255-8