Universal genetic code evidenced in mitochondria ofChlamydomonas reinhardii

Summary With the ultimate intent to establish a transformation system for eukaryotic organelles, the structure and organization of mitochondrial genes from the unicellular algaChlamydomonas reinhardii has been investigated. Using DNA hybridisation and DNA sequencing techniques, 3.9 kb of DNA, comprising about 25% of the mitochondrial genome, have been analysed in detail. By comparing the primary structure of homologous genes from other eukaryotic systems, we were able to identify the continuous genes coding for cytochrome oxidase subunit I (COI) and a NADH dehydrogenase subunit (ND5). The two genes are coded by opposite DNA strands and are not overlapping. The COI and the ND5 genes code for 505 and 567 amino acids, respectively. Interestingly, the comparative analysis with homologous genes from other eukaryotes shows that the universal genetic code is used in mitochondria ofC. reinhardii. This situation is different from all other mitochondrial systems studied so far. The results provide evidence thatC. reinhardii would be the appropriate organism for development of a transformation and expression system, where foreign genes, translated via the universal genetic code, are introduced into mitochondria.