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Gene Review

psaB  -  PSI P700 apoprotein A2

Chlamydomonas reinhardtii

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High impact information on psaB

  • Tab2 is a novel conserved RNA binding protein required for translation of the chloroplast psaB mRNA [1].
  • Directed mutagenesis indicates the importance of a highly conserved C-terminal tripeptide in Tab2 for normal psaB translation [1].
  • Insertion of these genes into the chloroplast genome through biolistic transformation and analysis of their expression in the TAB1 mutant nuclear background revealed that the psaB (but not the psaA) 5' UTR is the target of the wild-type TAB1 function [2].
  • The dependence of PSAA synthesis or accumulation on PSAB synthesis is strongly suggested by the identification of a suppressor mutation within the psaB 5' UTR [2].
  • This suggests that TAB1 is required for the initiation of psaB mRNA translation [2].

Biological context of psaB

  • Plasmids containing mutated copies of the chloroplast psaB gene, encoding a polypeptide of the photosystem I reaction center heterodimer, were introduced into the chloroplast genome by particle bombardment [3].
  • The first involved complementation of a nonphotosynthetic mutant of Chlamydomonas, CC-2341 (ac-u-g-2.3), which has a frameshift mutation in the psaB gene, and selection of photosynthetic transformants on minimal medium [3].
  • These experiments along with sequence analysis disclosed the presence, in both green algae, of a single IA1 intron in the psaB gene and of two group I introns (IA2 and IA1) in the psbC gene [4].
  • Thus, the 3' flanking regions of the rbcL and psaB genes can define the location of the 3' terminus of a transcript in vivo [5].
  • Transformants harboring chimeric GUS genes fused to rbcL or psaB gene 3' inverted repeat sequences in their normal forward orientations accumulated GUS transcripts of a single size, whereas GUS transcripts of heterogenous sizes accumulated in transformants harboring the same gene lacking an inverted repeat sequence at its 3' end [5].

Anatomical context of psaB

  • The results are consistent with a link between polysome association, active synthesis and stability of psaB transcripts [6].

Associations of psaB with chemical compounds

  • By measuring O2 and CO2 exchange in mutants of the green alga Chlamydomonas reinhardtii in which genes encoding the reaction center of photosystem I (psaA or psaB) have been deleted, we found that a photosystem II-dependent electron flow using O2 as the final acceptor can be sustained in the light [7].

Other interactions of psaB

  • The atpA, atpB and psaB mRNAs were most abundant in the first 6 hours of the light period and decreased to about 15% of maximum in the dark [8].
  • The IA1 introns in psaB and psbC were found to be related in sequence to the first intron in the C. moewusii chloroplast psbA gene [4].
  • However, both the atpB and the psaB sequence data gave robust support for a rather different set of phylogenetic relationships in which neither the "pyrenoid-lost" nor the "pyrenoid-regained" clade was resolved [9].

Analytical, diagnostic and therapeutic context of psaB


  1. Tab2 is a novel conserved RNA binding protein required for translation of the chloroplast psaB mRNA. Dauvillée, D., Stampacchia, O., Girard-Bascou, J., Rochaix, J.D. EMBO J. (2003) [Pubmed]
  2. A nuclear-encoded function essential for translation of the chloroplast psaB mRNA in chlamydomonas. Stampacchia, O., Girard-Bascou, J., Zanasco, J.L., Zerges, W., Bennoun, P., Rochaix, J.D. Plant Cell (1997) [Pubmed]
  3. Site-directed mutagenesis of the photosystem I reaction center in chloroplasts. The proline-cysteine motif. Webber, A.N., Gibbs, P.B., Ward, J.B., Bingham, S.E. J. Biol. Chem. (1993) [Pubmed]
  4. Group I introns interrupt the chloroplast psaB and psbC and the mitochondrial rrnL gene in Chlamydomonas. Turmel, M., Mercier, J.P., Côté, M.J. Nucleic Acids Res. (1993) [Pubmed]
  5. Functional in vivo analyses of the 3' flanking sequences of the Chlamydomonas chloroplast rbcL and psaB genes. Blowers, A.D., Klein, U., Ellmore, G.S., Bogorad, L. Mol. Gen. Genet. (1993) [Pubmed]
  6. Increased mRNA accumulation in a psaB frame-shift mutant of Chlamydomonas reinhardtii suggests a role for translation in psaB mRNA stability. Xu, R., Bingham, S.E., Webber, A.N. Plant Mol. Biol. (1993) [Pubmed]
  7. Limited photosynthetic electron flow but no CO2 fixation in Chlamydomonas mutants lacking photosystem I. Cournac, L., Redding, K., Bennoun, P., Peltier, G. FEBS Lett. (1997) [Pubmed]
  8. Cell cycle-dependent transcriptional and post-transcriptional regulation of chloroplast gene expression in Chlamydomonas reinhardtii. Leu, S., White, D., Michaels, A. Biochim. Biophys. Acta (1990) [Pubmed]
  9. Differences in pyrenoid morphology are correlated with differences in the rbcL genes of members of the Chloromonas lineage (volvocales, chlorophyceae). Nozaki, H., Onishi, K., Morita, E. J. Mol. Evol. (2002) [Pubmed]
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