GENETIC INTERACTION BETWEEN YPT6 AND YPT1 IN SACCHAROMYCES-CEREVISIAE

Ypt6p, the yeast homologue of human RAB6, is required for protein traf ficking at elevated temperatures. Biochemical data provide evidence th at Ypt6p plays a role in an early step(s) of the secretory pathway: fr om ER to Golgi, or from cis to medial Golgi, or both. Here we show tha t overexpression of YPT1 suppresses the growth and secretion defects o f a ypt6 temperature-sensitive (ts) strain. SLY1-20, encoding a domina nt mutant allele that suppresses the lethal effect of YPT1, also suppr esses the growth defect of a ypt6 ts strain. Conversely, SSD1, isolate d as a suppressor of ypt6 ts, can suppress the growth defect of a ypt1 ts allele. These data suggest that Ypt6p has some redundant function with Ypt1p. However, overexpression of Ypt6p is toxic to a ypt1 ts str ain, although it does not affect the growth of wild-type cells, sugges ting that Ypt6p may sequester proteins shared with Ypt1p. This genetic evidence confirms the conclusion that Ypt6p is involved in an early s tep of the secretory pathway. (C) 1998 John Whey & Sons, Ltd.