The complete nucleotide sequence of the mitochondrial genome of a very primitive unicellular red alga, Cyanidioschyzon merolae, has been determined. The mitochondrial genome of C.merolae contains 34 genes for proteins including unidentified open reading frames (ORFs) (three subunits of cytochrome c oxidase, apocytochrome b protein, three subunits of F1F0-ATPase, seven subunits of NADH ubiquinone oxidoreductase, three subunits of succinate dehydrogenase, four proteins implicated in c-type cytochrome biogenesis, 11 ribosomal subunits and two unidentified open reading frames), three genes for rRNAs and 25 genes for tRNAs. The G+C content of this mitochondrial genome is 27.2%, The genes are encoded on both strands. The genome size is comparatively small for a plant mitochondrial genome (32 211 bp), The mitochondrial genome resembles those of plants in its gene content because it contains several ribosomal protein genes and ORFs shared by other plant mitochondrial genomes, In contrast, it resembles those of animals in the genome organization, because it has very short intergenic regions and no introns, The gene set in this mitochondrial genome is a subset of that of Reclinomonas americana, an amoeboid protozoan, The results suggest that plant mitochondria originate from the same ancestor as other mitochondria and that most genes were lost from the mitochondrial genome at a fairly early stage of the evolution of the plants.
