Fig. 1. Cognate v-SNAREs were mistargeted in HeLa cells expressing syntaxin 1. (A) HeLa cells transfected with syntaxin 1 were fixed and double stained for syntaxin 1 and for the endogenous ER marker calreticulin. Insets show confocal images acquired at high magnification of a syntaxin-1-expressing cell. Note the colocalization between syntaxin 1 and calreticulin. (B,C) HeLa cells transfected with syntaxin 1 or co-transfected with syntaxin 1 and nSec1 as indicated were fixed and double stained for syntaxin 1 and endogenous TI-VAMP, cellubrevin (Cb) or endobrevin (Eb). Transfected cells are marked with an asterisk. A non-transfected cell in C (low panel) is indicated with a triangle. Note that TI-VAMP vesicular staining was lost in cells expressing syntaxin 1 alone but not in those co-expressing syntaxin 1 and nSec1. In syntaxin-1-expressing cells the perinuclear enrichment characteristic of cellubrevin (arrows) was also lost. By contrast, endobrevin vesicular staining was unaffected. Bar, 6 µm. Bar in the inset, 2.5 µm.