Electron microscopic analysis of sec2-78, wild-type, and sec6-4 cells labeled for Sec4p with immunogold. Cells were grown
overnight at 25°C, shifted to 37°C for 30 min, and then prepared for postembedding immunogold labeling as described in Materials and
Methods. (A) A sec2-78 (NY1529) cell grown at the permissive temperature where some immunogold labeling is found on vesicles in the
bud. Both wild-type (NY10, C) and sec6-4 (NY1294, D) cells show a concentration of immunogold labeling on vesicles in the bud after
shift to the restrictive temperature. In contrast, an average sec2-78 cell in B has immunogold-labeled vesicles randomly distributed in the
bud and mother cell. At 25°C (A) 3 ± 2 gold particles were observed on vesicles while 3 ± 2 gold particles were found independent of
vesicles in the bud. In the mother cell were 1 ± 1 gold particle on vesicles and 10 ± 3 gold particles not on vesicles. At 37°C (B) we found
3 ± 2 gold particles on vesicles and 3 ± 4 gold particles not on vesicles in the bud. In the mother cell were 4 ± 3 gold particles on vesicles
and 15 ± 9 gold particles not on vesicles. The error represents the SD for n = 12 at 25°C and n = 24 at 37°C. Bar, 1 μm.