RNA editing in Arabidopsis mitochondria effects 441 C to U changes in ORFs

On the basis of the sequence of the mitochondrial genome in the flowering p lant Arabidopsis thaliana, RNA editing events were systematically investiga ted in the respective RNA population. A total of 456 C to U, but no U to C, conversions were identified exclusively in mRNAs. 441 in ORFs, 8 in intron s, and 7 in leader and trailer sequences. No RNA editing was seen in any of the rRNAs or in several tRNAs investigated for potential mismatch correcti ons. RNA editing affects individual coding regions with frequencies varying between 0 acid 18.9% of the codons, The predominance of RNA editing events in the first two codon positions is not related to translational decoding, because it is not correlated with codon usage. As a general effect, RNA ed iting increases the hydrophobicity of the coded mitochondrial proteins. Con cerning the selection of RNA editing sites, little significant nucleotide p reference is observed in their vicinity in comparison to unedited C residue s. This sequence bias is, per se, not sufficient to specify individual C nu cleotides in the total RNA population in Arabidopsis mitochondria.