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Plant J. 2012 Nov;72(4):652-61. doi: 10.1111/j.1365-313X.2012.05111.x. Epub 2012 Sep 13.

Identification of an OPR protein involved in the translation initiation of the PsaB subunit of photosystem I.

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Departments of Molecular Biology and Plant Biology, University of Geneva, 30, Quai Ernest Ansermet, Geneva 1211, Switzerland.


Genetic analysis of mutants deficient in the biosynthesis of the photosystem I complex has revealed several nucleus-encoded factors that act at different post-transcriptional steps of chloroplast gene expression. Here we have identified and characterized the gene affected in the tab 1-F15 mutant, which is specifically deficient in the translation of the photosystem I reaction center protein PsaB as the result of a single nucleotide deletion. This gene encodes Tab 1, a 1287 amino acid protein that contains 10 tandem 38-40 amino acid degenerate repeats of the PPPEW/OPR (octatricopeptide repeat) family, first described for the chloroplast translation factor Tbc2. These repeats are involved in the binding of Tab 1 to the 5'-untranslated region of the psaB mRNA based on gel mobility shift assays. Tab 1 is part of a large family of proteins in Chlamydomonas that are also found in several bacteria and protozoans, but are rare in land plants.

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