9.B.63 The Yeast Pheromone-induced Plasma Membrane Mating Cell Fusion Protein (PRM1) Family 

Prm1 is a pheromone-regulated membrane glycoprotein involved in the plasma membrane fusion event that occurs during Saccharomyces cerevisiae mating. Although this function suggests that Prm1 should act at contact sites in pairs of mating yeast cells where plasma membrane fusion occurs, only a small percentage of the total Prm1 is detected on the plasma membrane. Olmo and Grote 2010 therefore investigated the intracellular transport of Prm1 and how this transport contributes to cell fusion. Two Prm1 chimeras that were sorted away from the contact site had reduced fusion activity, indicating that Prm1 indeed functions at contact sites. However, most Prm1 is located in endosomes and other cytoplasmic organelles and is targeted to vacuoles for degradation. Under all mating conditions, a pool of Prm1 was retained at polarized sites on the plasma membrane and was sufficient to promote plasma membrane fusion.  Prm1 is also required for fusion in fission yeast (Curto et al. 2014). Kex2 and Kex1golgi-resident proteases may promote cell fusion by proteolytically processing one or more protein(s) that act in parallel to Prm1 as an alternative fusion machine (Heiman et al. 2007).