The deduced primary structure of subunit I from cytochrome c oxidase suggests that the genus Polytomella shares a common mitochondrial origin with Chlamydomonas.

We cloned and sequenced the mitochondrial gene encoding subunit I of cytochrome c oxidase (coxI) of Polytomella spp., a colorless alga related to Chlamydomonas. The purpose was to explore whether homology between the two species also exists at the level of a mitochondrial enzyme. The gene is 1512 bp long and contains no introns. The translated protein sequence exhibits 73.8% identity with its Chlamydomonas reinhardtii counterpart. The data obtained support the hypothesis that the separation of the colorless alga from the Chlamydomonas lineage was a late event in evolution, that occurred after the endosymbiotic process that gave rise to mitochondria.