Protein Disulfide Isomerase as a Regulator of Chloroplast Translational Activation

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Abstract
Light-regulated translation of chloroplast messenger RNAs (mRNAs) requires trans-acting factors that interact with the 5′ untranslated region (UTR) of these mRNAs. Chloroplast polyadenylate-binding protein (cPABP) specifically binds to the 5′-UTR of the psbA mRNA and is essential for translation of this mRNA. A protein disulfide isomerase that is localized to the chloroplast and copurifies with cPABP was shown to modulate the binding of cPABP to the 5′-UTR of the psbA mRNA by reversibly changing the redox status of cPABP through redox potential or adenosine 5′-diphosphate–dependent phosphorylation. This mechanism allows for a simple reversible switch regulating gene expression in the chloroplast.