An antiserum against a glycoprotein functional in flagellar adhesion between Chlamydomonas eugametos gametes.

Chlamydomonas eugametos gametes agglutinate sexually by their flagellar surfaces. The agglutination factor on mating type minus (mt-) gametes is thought to be a glycoprotein named PAS-1.2. To test this idea, an antiserum was raised against purified PAS-1.2, which reacted with isolated PAS-1.2 (immunoprecipitation tests) and blocked the ability of isolated PAS-1.2 to induce sexual twitching in mt+ gametes. When tested with living cells, the antiserum specifically agglutinated mt- gametes and induced a reaction resembling twitching. Mt+ flagella were shown to bind the antiserum (indirect immunofluorescence) but much less than mt- gametes. Mt- gametes pretreated with Fab fragments of the antiserum were unable to reproduce sexually, while treated mt+ gametes were unaffected. This effect presumably results from the ability of the serum to block mt- sexual agglutination, for mt- isoagglutinin was completely inactivated by the serum, while mt+ isoagglutinin was unaffected. It is therefore argued that PAS-1.2 is the in vivo mt- agglutination factor. However it is shown that the antiserum was able to react in vitro not only with PAS-1.2 but with several other proteins in both mt- and mt+ flagella.