Sexual Agglutination in the Unicellular Green Alga Chlamydomonas eugametos: Identification and Properties of the Mating Type plus Agglutination Factor

Gametes of the unicellular green alga Chlamydomonas eugametos agglutinate via their flagella. The mating type plus agglutination factor was solubilized by relatively mild treatments such as a short pH shock or an osmotic shock indicating that it is an extrinsic membrane component. It was also extracted in the nonionic detergent Triton X-100. A simple two-step procedure consisting of gel filtration over Sepharose 4B-cross-linked followed by anion exchange chromatography of the void volume yielded an electrophoretically pure preparation of a single high molecular weight glycoprotein. The agglutination factor sedimented as a 9.3 S particle (assuming a density of 1.50) in sucrose gradients. This low value, compared with the high apparent molecular weight seen during gel filtration and electrophoresis, suggests that the agglutination factor is a rod-like molecule. This was confirmed by viewing rotary-shadowed preparations in the electron microscope. A population of long slender molecules was revealed (328 ± 20 nanometers), many of which had a knob at one end and a flexible region about one fourth of the length from the other end.