A GENE CODING FOR AN RPS2 PROTEIN IS PRESENT IN THE MITOCHONDRIAL GENOME OF SEVERAL CEREALS, BUT NOT IN DICOTYLEDONS

A gene coding for a protein that shows homologies to prokaryotic ribos omal protein S2 is present in the mitochondrial (mt) genome of wheat ( Triticum aestivum). The wheat gene is transcribed as a single mRNA whi ch is edited by C-to-U conversions at seven positions, all resulting i n alteration of the encoded amino acid. Homologous gene sequences are also present in the mt genomes of rice and maize, but we failed to ide ntify the corresponding sequences in the mtDNA of all dicotyledonous s pecies tested; in these species the mitochondrial RPS2 is probably enc oded in the nucleus. The protein sequence deduced from the wheat rps2 gene sequence has a long C-terminal extension when compared to other p rokaryotic RPS2 sequences. This extension presents no similarity with any known sequence and is not conserved in the maize or rice mitochond rial rps2 gene. Most probably, after translation, this peptide extensi on is processed by a specific peptidase to give rise to the mature whe at mitochondrial RPS2.