Fig. 1. SNAP-25 but not syntaxin traffics readily to the plasma membrane in live cells, but ectopic complexes can form. (A) Live N2a cells expressing Syx_1-288, Syx_1-288 coexpressed with munc18-1, Syx_1-288[open] or Syx_1-288[open] coexpressed with munc18-1. The FLIM data confirmed that Syx_1-288 and Syx_1-288[open] interact with munc18-1. (B) Fields of PC12 cells expressing the same constructs were scored for syntaxin trafficking to the cell surface. The percentage of cells with surface syntaxin was plotted. (C) N2a cells expressing SNAP-25_1-206 or truncated SNAP-25_1-121 were imaged by CLSM. Shown are representative equatorial sections; n>20 images. Bar, 10 µm. (D) Wild-type or mutant SNAP-25_1-206 (green) and Syx_1-288 (red) were expressed in live N2a cells and imaged by CLSM, as before. The merged image shows areas of coincidence in yellow hues. The two-dimensional histogram represents the intensity of each channel in each voxel, with a colour scale representing frequency. The residual map corresponds to weighted residuals from the linear regression of the histogram, thus indicating fluorescent channel covariance. The hue is from –1 to 1, with cyan corresponding to a zero residual. Shown are representative equatorial sections; n>20 images. Bar, 5 µm.