Surface display of a parasite antigen in the ciliate Tetrahymena thermophila

The ciliated protozoan, Tetrahymena thermophila, offers an attractive mediu m for the expression of heterologous proteins and could prove particularly useful for the display of foreign proteins on the cell surface. Although pr ogress has been made in transformation of Tetrahymena with heterologous DMA , methods that permit reliable expression of foreign genes have been lackin g. Using a mutant strain of T: thermophila carrying a negatively selectable allele of a beta-tubulin gene, we have been able to direct foreign genes t o this locus by homologous recombination. Transformed cell lines producing foreign proteins were readily identified and, in at least one case, targeti ng of proteins to the plasma membrane was accomplished.