Self from nonself discrimination in single-celled eukaryotes.

A mechanism for self recognition has been proposed to control the mating type interactions in the marine ciliate Euplotes raikovi. The relevant molecules involved in this mechanism are the mating pheromones inherited via high-multiple alleles codominant at the Mendelian locus mat. Four of these mating pheromones have been isolated, purified, and characterized. They are relatively small and acidic proteins (Mr, 11,000-12,000; pI, 3.7-4.0), which are still active at the concentration of approximately 10(-12) molar. Data, yet preliminary, of amino acid sequencing of the purified mating pheromones showed extensive structural homologies and the common presence of the aspartic acid at the amino terminal.