LECTIN-BINDING SITES INVOLVED IN PARAMECIUM-PRIMAURELIA MATING PAIR FORMATION

Mating pair formation in Paramecium primaurelia was shown to be inhibi ted by incubating mating-competent mating type (mt) I and mt II cells with Limulus polyphemus agglutinin (LPA) or wheat germ agglutinin (WGA ). Preincubation of LPA and WGA with their specific binding-monosaccha rides, N-acetylneuraminic acid (NeuAc) and N-acetylglucosamine (GlcNAc ), respectively, prevented the lectin effect on pair formation. Additi on either of NeuAc or GlcNAc resulted in a reversal of cell pairing in hibition by LPA or WGA, respectively. Both NeuAc and GlcNAc monosaccha rides inhibited pair formation when their concentration exceeded a thr eshold value. The pattern of the relative distribution of NeuAc and Gl cNAc molecules on the cell surface was analyzed using fluorescence res onance energy transfer techniques combined with imaging systems. Mt II cells showed a high lectin-binding site density localized just on the surface region engaged in conjugation. The pattern of mt I cells, con sisting of a quite homogeneous lectin-binding site density spread on t he cell surface, was also common to nonmating-competent cells and to i mmature cells. These findings suggest that in P. primaurelia pair form ation involves both NeuAc and GlcNAc residues and that the development of mating-competence is related to a modification in NeuAc and GlcNAc relative distribution on the cell surface of mt II cells.