A SEX RECOGNITION GLYCOPROTEIN IS ENCODED BY THE PLUS MATING-TYPE GENE FUS1 OF CHLAMYDOMONAS-REINHARDTII

Sexual fusion between plus and minus gametes of the unicellular green alga Chlamydomonas reinhardtii entails adhesion between plus-specific and minus-specific ''fringe'' proteins displayed on the plasma membran e of gametic mating structures. We report the identification of the ge ne (fus1) encoding the plus fringe glycoprotein, which resides in a un ique domain of the mating-type plus (mt(+)) locus, and which was ident ified by transposon insertions in three fusion-defective mutant strain s. Transformation with fus1(+) restores fringe and fusion competence t o these mutants and to the pseudo-plus mutant imp11 mt(-), defective i n minus differentiation. The fus1 gene is remarkable in lacking the co don bias found in all other nuclear genes of C. reinhardtii.