The phylogenetic position of alpha- 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 characterised. We found the Cercomonas and Chlorarachnion alpha tubulins to be closely related to one another, confirming the proposed relationship of these genera. In addition, the Chlorarachnion host and Cercomonas also appear to be more distantly related to Heterolobosea, Euglenozoa, chlorophytes, heterokonts, and alveolates. Chlorarachnion was also found to have two distinctly different types of both alpha- and beta-tubulin, one type being highly-divergent. Chlorarachnion contains a secondary endosymbiont of green algal origin, raising the possibility that one type of Chlorarachnion tubulins comes from the host and the other from the endosymbiont. Probing pulsed field-separated chromosomes showed that the highly-divergent genes are encoded by the host genome, and neither alpha- nor beta-tubulin cDNAs were found to include 5' extensions that might serve as targeting peptides. It appears that Chlorarachnion has distinct and divergent tubulin paralogues that are all derived from the host lineage. One Chlorarachnion beta-tubulin was also found to be a pseudogene, which is still expressed but aberrantly processed. Numerous unspliced introns and deletions resulting from mis-splicing are contained in the mRNAs from this gene.