The alpha- and beta-tubulin genes of Euplotes octocarinatus

The alpha- and the beta-tubulin genes of the hypotrichous ciliate Euplotes octocarinatus were isolated from a size-selected macronuclear DNA library. The alpha-tubulin gene is located on a 1,587 bp macronuclear DNA molecule and the beta-tubulin gene on a 1,524 bp macronuclear DNA molecule. Sequencing revealed that all the cysteine residues of the two genes are encoded by the common cysteine codons UGU and UGC and none by an UGA codon. This is in contrast to the genes of E. octocarinatus sequenced so far, where some of the cysteines are encoded by the opal codon UGA. The tubulin genes end like other Euplotes genes with a TAA. They do not contain introns. The last codon for an amino acid in the alpha-tubulin gene is a GAA which codes for glutamic acid. This is in contrast to what has been reported for most alpha-tubulin genes, but it supports for other hypotrichous ciliates. No evidence for the existence of more than one type of alpha- and one type of beta-tubulin genes could be obtained.