Characterization of two genes encoding a fifth so far unknown pheromone of Euplotes octocarinatus

Summary Two new stocks of the hypotrichous ciliate Euplotes octocarinatus isolated in Pennsylvania and Florida/USA were identified as members of a new mating type XI (mt 5 mt 5 ) secreting a so far unknown pheromone 5. As deduced from their pheromone encoding genes, the pheromones secreted by the two stocks differ from each other by 14 amino acids and a few silent mutations. Their 5′-non-coding sequences are almost identical with the 5′-non-coding sequences of the pheromone genes 1 to 4. This holds also true for the prepro-sequences which contain a 16 amino acids long ER-import signal. The 3′-non-coding sequences are also highly conserved. Like the other pheromone encoding genes the two mt 5 alleles contain in-frame TGA stop codons, probably encoding cysteines. Both genes are interrupted by three introns in positions which are homologous to those in the other pheromone genes. Intron 1 of the stock from Florida is 143 bp longer than intron 1 of the stock from Pennsylvania. Indirect evidence suggests that the two stocks do not belong to E. octocarinatus syngen 1. In this respect the two stocks resemble two other stocks isolated in North America which we have previously investigated. Whether the two stocks belong to the same syngens as the other two North American stocks is unclear.