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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.

Cellular localization of green fluorescent protein (GFP) fused with the transit peptide of CRR4.

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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