RNA EDITING IN PLANT-MITOCHONDRIA AND CHLOROPLASTS

In the mitochondria and chloroplasts of higher plants there is an RNA editing activity responsible for specific C-to-U conversions and for a few U-to-C conversions leading to RNA sequences different from the co rresponding DNA sequences. RNA editing is a post- transcriptional proc ess which essentially affects the transcripts of protein coding genes, but has also been found to modify non-coding transcribed regions, str uctural RNAs and intron sequences. RNA editing is essential for correc t gene expression: proteins translated from edited transcripts are dif ferent from the ones deduced from the genes sequences and usually pres ent higher similarity to the corresponding non-plant homologues. Initi ation and stop codons can also be created by RNA editing. RNA editing has also been shown to be required for the stabilization of the second ary structure of introns and tRNAs. The biochemistry of RNA editing in plant organelles is still largely unknown. In mitochondria, recent ex periments indicate that RNA editing may be a deamination process. A pl astid transformation technique showed to be a powerful tool for the st udy of RNA editing. The biochemistry as well as the evolutionary featu res of RNA editing in both organelles are compared in order to identif y common as well as organelle-specific components.