The role of surface filaments in the cell agglutination of the yeast Hansenula wingei



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The heterothallic yeast Hansenula wingei is a favorable organism for the study of specific cell adhesion which, in this system, is termed sexual agglutination. Previous investigations have shown that cell agglutinability may be activated by either chemical or physical treatments. Activation of the cells was accomplished either by addition of cations or by heat treatment. Using a rapid whole-cell radioassay technique, several aspects of cation activation were studied. The comparative effect of cations in activation established the following series: trivalent> divalent> monovalent. With each of these categories of valence, all tested cations were equal in effect. The action of cations in activation was attributed to a reduction in repulsive forces due to the titration of negatively charged sites at the cell periphery so that the active adhesive components could come sufficiently close for short range attractive forces to function. Several non-agglutinating mutants were also isolated and characterized with respect to cation binding ability and cell surface morphology. It was also shown that heat activation removed the highly negatively charged surface fringe. In addition, the morphology of the actual areas of contact between apposed cells was described. Evidence from several areas supported a two-site model for the localization of the agglutination factors. These factors are located in or on filaments in the surface fringe and outer layer of the cell wall.



Yeast, Conjugation (Biology), Agglutination