THE PHYLOGENETIC POSITION OF ALPHA-TUBULINS AND BETA-TUBULINS FROM THE CHLORARACHNION HOST AND CERCOMONAS (CERCOZOA)

Alpha and beta-tubulin genes from Chlorarachnion and an alpha-tubulin gene from Cercomonas have been characterized We found the Cercomonas a nd Chlorarachnion alpha-tubulins to be closely related to one another, confirming the proposed relationship of these genera. In addition, th e Chlorarachnion host and Cercomonas also appear to be more distantly related to Heterolobosea, Euglenozoa, chlorophytes, heterokonts, and a lveolates. Chlorarachnion was also found to have two distinctly differ ent types of both alpha- and beta-tubulin, one type being highly-diver gent. Chlorarachnion? contains a secondary endosymbiont of green algal origin, raising the possibility that one type of Chlorarachnion tubul ins comes from the host and the other from the endosymbiont. Probing p ulsed field-separated chromosomes showed that the highly-divergent gen es are encoded by the host genome, and neither alpha- nor beta-tubulin cDNAs were found to include 5' extensions that might serve as targeti ng peptides. It appears that Chlorarachnion has distinct and divergent tubulin paralogues that are all derived from the host lineage. One Ch lorarachnion beta-tubulin was also found to be a pseudogene, which is still expressed but aberrantly processed. Numerous unspliced introns a nd deletions resulting from mis-splicing are contained in the mRNAs fr om this gene.