Figure 2.

SNARE complex assembly and secretion in exocyst mutant yeast. (a) Variation in SNARE complex amounts with time at 38°C. Wild-type (NY13) cells grown at 25°C were incubated at 38°C for the indicated times. Coimmunoprecipitation of Ssop with Sncp was quantified as described in the legend to Fig. 1 b. The amount of Ssop bound to Sncp at 25°C was defined as 100%. (b) SNARE complex assembly. sec5-24 (NY402), sec6-4 (NY7), sec8-6 (NY47), sec 10-2 (NY61), and sec15-1 (NY64) cells grown at 25°C were incubated at 38°C for the indicated times. The amount of Ssop bound to Sncp in the wild-type at each time point was defined as 100%. (c) Positive correlation between SNARE complex assembly and the secretion rate. Release of ³⁵S-p150 from cells labeled with [³⁵S]methionine at 38°C was quantified by PhosphorImager as described in the legend to Fig. 1 d. The rate of secretion from 4 to 12 min after [³⁵S]methionine addition is plotted. In all strains tested, the secretion rate was constant after the 4 min required for biosynthesis and transport of ³⁵S-labeled proteins through the secretory pathway. The secretion rate in wild-type cells at 38°C was defined as 100%. The amount of Ssop bound to Sncp after 10 min at 38°C (from b) is also displayed to facilitate comparisons.