Purification and initial characterization of two pheromones from the marine Antartic cilate, Euplotes nobilii

Among a set of wild-type strains of Euplotes nobilii, every one derived asexually from one specimen isolated from Terra Nova Bay (Ross Sea, Antarctica), two were found to be representative of different mating types mutually capable of inducing each other to form mating pairs through pheromones constitutively secreted into the extracellular environment. Pheromones of strain AC-1 were purified to homogeneity and shown to be represented by two distinct proteins, that were denoted En-1 and En-2. En-1, secreted in amounts three-fold greater than En-2, was determined to have a molecular weight of 5617 and an asparagine at the N-terminus of its amino acid sequence, while En-2 has a molecular weight of 6290 and bears an asparctic acid at its N-terminus. The fact that En-1 and En-2 are coreleased by genetically identical cells of the same strain was taken to imply that they carry a heterozygotic combination of allelic pheromone genes and that these genes are regulated by relationships of co-dominance.