Mitochondria are genetic compartments with their own enzymatic equipment for maintenance and expression of their genetic information. As in all genetic systems, gene expression has to be regulated, and in mitochondria this also has to be coordinated with the expression of nuclear-encoded mitochondrial proteins. Presently, there is virtually no information available about the mechanistic details and the enzymes involved in these processes. There is still much to be learned about how plant mitochondrial gene expression is managed and to what extent the contribution of transcription initiation and posttranscriptional processes, respectively, contribute to this control. As one prerequisite for better understanding of the mechanisms and regulatory controls, more fundamental data on mitochondrial transcription initiation and posttranscriptional RNA processing are necessary. As part of the essential methodology, we present methods for the analysis of the 5′ and 3′ extremities of mitochondrial transcripts and the identification of transcription initiation sites. Anin organellosystem is described for the functional investigation of ribonucleic acid editing in plant mitochondria.
