Distribution of the mitochondrial deviant genetic code AUA for methionine in heterokont algae

The DNA sequence of the cytochrome oxidase subunit I (COXI) gene (1059 bp), was determined in a number of heterokont algae, including five species of the Phaeophyceae [Chorda filum (Linnaeus) Stackhouse, Colpomenia bullosa (S aunders) Yamada, Ectocarpus sp., Pseudochorda nagaii (Tokida) Inagaki, Unda ria pinnatifida (Harvey) Suringar], and a member of the Raphidophyceae [Cha ttonella antiqua (Hada) Ono]. The distribution of a deviant mitochondrial c ode, the AUA codon for methionine (AUA/Met), which was previously reported in the Xanthophyceae, was inferred from these COXI sequences. Comparative a nalyses of these sequences revealed that all the algae described above bear the universal genetic code, including the assignment for the AUA codon. A phylogenetic tree was constructed using the obtained sequences along with a lready-published COXI sequences of various heterokont algae. The clusters o f the Xanthophyceae and the Phaeophyceae were resolved as sister groups wit h high bootstrap support, excluding a bacillariophycean species, a raphidop hycean species, and three species of the Eustigratophyceae. Taking the dist ribution of the deviant code and the COXI phylogenetic tree together, the g enetic code change most probably occurred in an ancestor of the Xanthophyce ae after it had branched off from the Phaeophyceae.