Novel requirements for HAP2/GCS1-mediated gamete fusion in .

The ancestral gamete fusion protein, HAP2/GCS1, plays an essential role in fertilization in a broad range of taxa. To identify factors that may regulate HAP2/GCS1 activity, we screened mutants of the ciliate for behaviors that mimic knockout phenotypes in this species. Using this approach, we identified two new genes, and , whose products are necessary for membrane pore formation following mating type recognition and adherence.