Identification of two beta-tubulin isotypes of Clonorchis sinensis

The beta-tubulin coding sequences were investigated for the Chinese liver fluke, Clonorchis sinensis. A cDNA library of adult C. sinensis was screened with cDNA probes synthesized by polymerase chain reaction using degenerate primers, and two beta-tubulin cDNAs, CsTB1 and CsTB3, were subsequently cloned. The CsTB1 and CsTB3 cDNA were 2,082 and 1,486 bp long and encoded 445 and 444 amino acids, respectively. The two clones were identical 78% in their coding sequences and 97% in deduced sequences. Moreover, the CsTB1 had 3'-UTR 592 bp longer than that of CsTB3. The CsTB1 and CsTB3 polypeptides were highly homologous (88-99%) with those of known beta-tubulins of other helminthes with a variation at the C-terminal region. In CsTB1 and CsTB3 polypeptides, two amino acids Tyr 200 and Phe 167 were conserved. The phylogenetic analysis of selected sequences indicates that the beta-tubulins can be organized into five groups and that the two beta-tubulin isotypes of C. sinensis are contained within one group with those of other trematodes and vertebrates.