A recombinase system facilitates cloning of expression cassettes in the ciliate Tetrahymena thermophila

Background: Tetrahymena thermophila is one of the best characterized unicellular eukaryotes and its genome is sequenced in its entirety. However, the AT-richness of the genome and an unusual codon usage cause problems in cloning and expression of the ciliate DNA. To overcome these technical hiatuses we developed a Cre-dependent recombinase system. Results: We created novel donor and acceptor vectors that facilitate the transfer of expression cassettes from the donor into novel acceptor plasmid. Expression vectors were used that encode the 19 kDa C-terminus of the MSP1 protein of Plasmodium falciparum and a blasticidin S (bsdR) resistance gene, respectively. The functional expression of these genes was demonstrated by western blot analysis with MSP1 specific antibodies and by a blasticidin growing assay. Conclusion: The Cre dependent recombinase system in combination with the modular structure of the donor vectors ease cloning and expression of foreign genes in the ciliate system, providing a powerful tool for protistology research in future.