THE ALPHA-TUBULIN AND BETA-TUBULIN GENES OF EUPLOTES-OCTOCARINATUS

The alpha- and the beta-tubulin genes of the hypotrichous ciliate Eupl otes octocarinatus were isolated from a size-selected macronuclear DNA library. The cu-tubulin gene is located on a 1,587 bp macronuclear DN A molecule and the beta-tubulin gene on a 1,524 bp macronuclear DNA mo lecule. Sequencing revealed that all the cysteine residues of the two genes are encoded by the common cysteine codons UGU and UGC and none b y an UGA codon. This is in contrast to the genes of E. octocarinatus s equenced so far, where some of the cysteines are encoded by the opal c odon 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 a lpha-tubulin gene is a GAA which codes for glutamic acid. This is in c ontrast to what has been reported for most alpha-tubulin genes, but it supports findings for other hypotrichous ciliates. No evidence for th e existence of more than one type of alpha- and one type of beta-tubul in genes could be obtained.