J. Biol. Chem., Vol. 281, Issue 49, 99940, December 8, 2006
RNA Editing Insights
RNA editing has puzzled scientists for a long time. In higher plants, the editing occurs as a post-transcriptional process that converts cytosine to uracil in mitochondria and plastid mRNAs. Recently, a pentatricopeptide repeat (PPR) protein, CRR4, was identified as a factor required for editing the initiation codon of the chloroplast ndhD transcript in Arabidopsis. Here, Kenji Okuda and colleagues describe experiments which clearly demonstrate that CRR4 is a sequence-specific RNA-binding protein capable of binding to the nucleotides surrounding the ndhD initiation codon.
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Cellular localization of green fluorescent protein (GFP) fused with the transit peptide of CRR4.
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The paper conclusively shows that the interaction between CRR4 and the editing site on the ndhD RNA is direct and that CRR4 acts as a site recognition factor in RNA editing. PPR proteins have often been touted as likely sequence-specific RNA-binding proteins, but results published previously have not been especially convincing or have been obtained under conditions where there was a possibility of the involvement of other sequence-specific binding proteins. This Paper of the Week contains the first results demonstrating the sequence-specific binding of a PPR protein to a physiologically relevant target RNA in vitro. Given the fact that there are some 450 PPR proteins in Arabidopsis, these results suggest that each PPR protein might bind specifically to a unique editing site.
FOOTNOTES
See referenced article, J. Biol. Chem. 2006, 281, 37661-37667 

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Copyright © 2006 by the American Society for Biochemistry and Molecular Biology.