LINEAGE-SPECIFIC EVOLUTION OF ECHINODERM MITOCHONDRIAL ATP-SYNTHASE SUBUNIT-8

Peculiar evolutionary properties of the subunit 8 of mitochondrial ATP synthase (ATPase8) are revealed by comparative analyses carried out b etween both closely and distantly related species of echinoderms. The analysis of nucleotide substitution in the three echinoids demonstrate d a relaxation of amino acid functional constraints. The deduced prote in sequences display a well conserved domain at the N-terminus, while the central part is very variable. At the C-terminus, the broad distri bution of positively charged amino acids, which is typical of other or ganisms, is not conserved in the two different echinoderm classes of t he sea urchins and of the sea stars. Instead, a motif of three amino a cids, so far not described elsewhere, is conserved in sea urchins and is found to be very similar to the motif present in the sea stars. Our results indicate that the N-terminal region seems to follow the same evolutionary pattern in different organisms, while the maintenance of the C-terminal part in a phylum-specific manner may reflect the co-evo lution of mitochondrial and nuclear genes.