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Gene Review

petA  -  apocytochrome f precursor

Chlamydomonas reinhardtii

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Disease relevance of petA

  • The difference in apparent molecular mass was maintained after expression of petA from both Chlamydomonas species in either E. coli or a C. reinhardtii DeltapetA mutant and after substitution of a unique third cysteine-292 to phenylalanine in the psychrophilic cytochrome f [1].
  • The structure of cytochrome f includes an internal chain of five water molecules and six hydrogen-bonding side chains, which are conserved throughout the phylogenetic range of photosynthetic organisms from higher plants, algae, and cyanobacteria [2].

High impact information on petA

  • The middle part of the Tbc2 protein displays partial amino acid sequence identity with Crp1, a protein from Zea mays that is implicated in the processing and translation of the chloroplast petA and petD RNAs [3].
  • To this end, we have constructed three deletion mutant strains, each lacking one of the major chloroplast pet genes: the delta petA, delta petB and delta petD strains were unable to synthesize cyt f, cyt b6 and subunit IV (suIV) respectively [4].
  • We have used a genetic approach to characterize the translocation of Chlamydomonas cytochrome f, a chloroplast-encoded protein that spans the thylakoid once [5].
  • Cytochrome f accumulated to detectable levels in all mutant strains except the one with a UUC codon, but only the mutant with an AUU codon grew well at 24 degrees C under conditions that require photosynthesis [6].
  • When expressed from a chimeric mRNA containing the atpA 5' untranslated region, cytochrome f no longer showed an assembly-dependent regulation of translation [7].

Biological context of petA

  • Nucleotide sequences of the continuous and separated petA, petB and petD chloroplast genes in Chlamydomonas reinhardtii [8].
  • We have mapped and sequenced the petA (cytf), petB (cytb6) and petD (subunit IV) genes on the chloroplast genome of Chlamydomonas reinhardtii [8].
  • A dominant mutant allele at this locus, sim30-1d, was found to increase the translation initiation rate of the mutant petD mRNA. sim30-1d was also able to suppress the translational defect caused by an AUG to AUC mutation in the petD gene, and an AUG to AUU mutation in the chloroplast petA gene [9].
  • We recovered one chloroplast suppressor in which the coding region of petA was now expressed under the control of a duplicated 5' untranslated region from another open reading frame of presently unknown function [10].
  • To determine whether this stem-loop was required for petA mRNA stability, a series of deletions was constructed [11].

Anatomical context of petA

  • In contrast, there was a decrease in polysome association of the polycistronic petA mRNA in the DeltapetB and DeltapetD mutants, suggesting that the synthesis of cytochrome f may be decreased in the absence of cytochrome b6 or SUIV [12].
  • Thylakoids of N-limited cells have reduced amounts of cytochrome b6, cytochrome f, and light-harvesting complexes [13].
  • Among the new polypeptides specifically found in the gametes, we detected a soluble polypeptide M alpha (approximate molecular mass of 63 kDa), which shared common epitopes with cytochrome f [14].
  • Here, we show that M alpha is not a modification product of cytochrome f, but is part of protein M, a high-molecular-mass L-amino-acid oxidase located in the periplasm [15].
  • Genetic analyses of Chlamydomonas reinhardtii ccs mutants, which are pleiotropically deficient in both the membrane-anchored cytochrome f and the soluble cytochrome c6, revealed a minimum of six loci, plastid ccsA and nuclear CCS1 through CCS5, that are required for the conversion of the chloroplast apocytochromes to their respective holo forms [16].

Associations of petA with chemical compounds

  • C. reinhardtii and S. obliquus complexes contain the Rieske iron-sulfur protein (present in approx 1:1 molar ratio to cytochrome f) and each catalyzes a DBMIB- and DNP-INT-sensitive electron transfer from duroquinol to spinach plastocyanin [17].
  • Its operation has been described by the "Q-cycle." This model proposes that electrons are transferred from plastoquinol to plastocyanin (the reductant of P700 in Photosystem I) through, obligatorily in series, the iron-sulfur and the cytochrome f redox centers in the cytochrome b(6)f complex [18].
  • The N-terminal tyrosine of cytochrome f, which provides the sixth ligand to the heme group, has been changed by site-directed mutagenesis in Chlamydomonas reinhardtii to evaluate the role of this amino acid in assembly and function [19].
  • The oxidation equivalents from Photosystem I are delivered to the high potential chain of the cytochrome b(6)f complex both at the cytochrome f level and, independently, at another site connected to the quinol-oxidizing site, possibly the iron-sulfur center [18].
  • The reduction of the potential by either decreasing the light intensity or by adding increasing concentrations of the ionophore carbonylcyanide p-(trifluoromethoxy)phenylhydrazone (FCCP) revealed a marked inhibition of the cytochrome b(6) oxidation rate (10-fold) without substantial modifications of cytochrome f oxidation kinetics [20].

Physical interactions of petA


Regulatory relationships of petA


Other interactions of petA

  • The resulting homoplasmic petG deletion strains are unable to grow photosynthetically, and immunoblot analysis shows markedly decreased levels of cytochrome b6, cytochrome f, the Rieske iron-sulfur protein, and subunit IV [22].
  • Synthetic RNAs of the petA 3' UTR and the antisense strand of atpB 3' UTR were degraded in the extract [23].
  • However, the C. reinhardtii petA transformants accumulated lower levels of cytochrome b ( 6 ) /f complexes and exhibited lower light saturated rates of O(2) evolution than C. reinhardtii wild type [1].

Analytical, diagnostic and therapeutic context of petA

  • The biosynthesis of cytochrome f is a multistep process which requires processing of the precursor protein and covalent ligation of a c-heme upon membrane insertion of the protein [24].
  • Unfolding of oxidized and reduced cytochrome f by guanidine hydrochloride (GuHCl) was monitored by far-UV circular dichroism (CD), Soret absorption, and tyrosine emission: the same unfolding curves were obtained regardless of method [25].
  • Although cytochrome f from the Antarctic psychrophile, Chlamydomonas raudensis UWO 241, exhibits a lower apparent molecular mass (34 kD) than that of the mesophile C. reinhardtii (41 kD) based on SDS-PAGE, both proteins are comparable in calculated molecular mass and show 79% identity in amino acid sequence [1].


  1. Cytochrome f from the Antarctic psychrophile, Chlamydomonas raudensis UWO 241: structure, sequence, and complementation in the mesophile, Chlamydomonas reinhardtii. Gudynaite-Savitch, L., Gretes, M., Morgan-Kiss, R.M., Savitch, L.V., Simmonds, J., Kohalmi, S.E., Hüner, N.P. Mol. Genet. Genomics (2006) [Pubmed]
  2. Interruption of the internal water chain of cytochrome f impairs photosynthetic function. Sainz, G., Carrell, C.J., Ponamarev, M.V., Soriano, G.M., Cramer, W.A., Smith, J.L. Biochemistry (2000) [Pubmed]
  3. Characterization of Tbc2, a nucleus-encoded factor specifically required for translation of the chloroplast psbC mRNA in Chlamydomonas reinhardtii. Auchincloss, A.H., Zerges, W., Perron, K., Girard-Bascou, J., Rochaix, J.D. J. Cell Biol. (2002) [Pubmed]
  4. The assembly of cytochrome b6/f complexes: an approach using genetic transformation of the green alga Chlamydomonas reinhardtii. Kuras, R., Wollman, F.A. EMBO J. (1994) [Pubmed]
  5. Mutations in a signal sequence for the thylakoid membrane identify multiple protein transport pathways and nuclear suppressors. Smith, T.A., Kohorn, B.D. J. Cell Biol. (1994) [Pubmed]
  6. The initiation codon determines the efficiency but not the site of translation initiation in Chlamydomonas chloroplasts. Chen, X., Kindle, K.L., Stern, D.B. Plant Cell (1995) [Pubmed]
  7. Translation of cytochrome f is autoregulated through the 5' untranslated region of petA mRNA in Chlamydomonas chloroplasts. Choquet, Y., Stern, D.B., Wostrikoff, K., Kuras, R., Girard-Bascou, J., Wollman, F.A. Proc. Natl. Acad. Sci. U.S.A. (1998) [Pubmed]
  8. Nucleotide sequences of the continuous and separated petA, petB and petD chloroplast genes in Chlamydomonas reinhardtii. Büschlen, S., Choquet, Y., Kuras, R., Wollman, F.A. FEBS Lett. (1991) [Pubmed]
  9. A dominant mutation in the Chlamydomonas reinhardtii nuclear gene SIM30 suppresses translational defects caused by initiation codon mutations in chloroplast genes. Chen, X., Simpson, C.L., Kindle, K.L., Stern, D.B. Genetics (1997) [Pubmed]
  10. TCA1, a single nuclear-encoded translational activator specific for petA mRNA in Chlamydomonas reinhardtii chloroplast. Wostrikoff, K., Choquet, Y., Wollman, F.A., Girard-Bascou, J. Genetics (2001) [Pubmed]
  11. Short dispersed repeats in the Chlamydomonas chloroplast genome are collocated with sites for mRNA 3' end formation. Jiao, H.S., Hicks, A., Simpson, C., Stern, D.B. Curr. Genet. (2004) [Pubmed]
  12. Post-transcriptional defects in tobacco chloroplast mutants lacking the cytochrome b6/f complex. Monde, R.A., Zito, F., Olive, J., Wollman, F.A., Stern, D.B. Plant J. (2000) [Pubmed]
  13. Chlororespiration: an adaptation to nitrogen deficiency in Chlamydomonas reinhardtii. Peltier, G., Schmidt, G.W. Proc. Natl. Acad. Sci. U.S.A. (1991) [Pubmed]
  14. Evidence for a selective destabilization of an integral membrane protein, the cytochrome b6/f complex, during gametogenesis in Chlamydomonas reinhardtii. Bulté, L., Wollman, F.A. Eur. J. Biochem. (1992) [Pubmed]
  15. Extensive accumulation of an extracellular L-amino-acid oxidase during gametogenesis of Chlamydomonas reinhardtii. Vallon, O., Bulté, L., Kuras, R., Olive, J., Wollman, F.A. Eur. J. Biochem. (1993) [Pubmed]
  16. A novel pathway for cytochromes c biogenesis in chloroplasts. Xie, Z., Merchant, S. Biochim. Biophys. Acta (1998) [Pubmed]
  17. Green algal cytochrome b6-f complexes: isolation and characterization from Dunaliella saline, Chlamydomonas reinhardtii and Scenedesmus obliquus. Wynn, R.M., Bertsch, J., Bruce, B.D., Malkin, R. Biochim. Biophys. Acta (1988) [Pubmed]
  18. Photosynthetic electron transfer through the cytochrome b6f complex can bypass cytochrome f. Fernández-Velasco, J.G., Jamshidi, A., Gong, X.S., Zhou, J., Ueng, R.Y. J. Biol. Chem. (2001) [Pubmed]
  19. N-terminal mutants of chloroplast cytochrome f. Effect on redox reactions and growth in Chlamydomonas reinhardtII. Zhou, J., Fernández-Velasco, J.G., Malkin, R. J. Biol. Chem. (1996) [Pubmed]
  20. Kinetic effects of the electrochemical proton gradient on plastoquinone reduction at the Qi site of the cytochrome b6f complex. Barbagallo, R.P., Breyton, C., Finazzi, G. J. Biol. Chem. (2000) [Pubmed]
  21. On the presence and role of a molecule of chlorophyll a in the cytochrome b6 f complex. Pierre, Y., Breyton, C., Lemoine, Y., Robert, B., Vernotte, C., Popot, J.L. J. Biol. Chem. (1997) [Pubmed]
  22. The deletion of petG in Chlamydomonas reinhardtii disrupts the cytochrome bf complex. Berthold, D.A., Schmidt, C.L., Malkin, R. J. Biol. Chem. (1995) [Pubmed]
  23. The sequence and structure of the 3'-untranslated regions of chloroplast transcripts are important determinants of mRNA accumulation and stability. Rott, R., Liveanu, V., Drager, R.G., Stern, D.B., Schuster, G. Plant Mol. Biol. (1998) [Pubmed]
  24. Maturation of pre-apocytochrome f in vivo. A site-directed mutagenesis study in Chlamydomonas reinhardtii. Kuras, R., Büschlen, S., Wollman, F.A. J. Biol. Chem. (1995) [Pubmed]
  25. Unfolding the unique c-type heme protein, Chlamydomonas reinhardtii cytochrome f. Sabahi, A., Wittung-Stafshede, P. Biochim. Biophys. Acta (2002) [Pubmed]
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