ER–ER fusion is delayed in cells missing Sey1p. (a) Wild-type cells of opposite mating types expressing either ss-RFP-HDEL or cytosolic GFP were mixed, placed on an agarose pad, and imaged at 1-min intervals. Selected images from the time-lapse video are shown. Time 0 is the first image taken after cell fusion, as indicated by GFP in both cells. The two cells of the analyzed mating pair are labeled 1 and 2. Bar, 1 µm. (b) Quantification of the RFP signal of cells 1 and 2 in a. (c) As in a, except that sey1Δ cells were used. (d) Quantification of the RFP signal of cells 1 and 2 in c. (e) A box and whiskers plot of the amount of time between cell fusion and ER fusion during mating. Top and bottom ends of the boxes represent the 75th and 25th percentiles, and whiskers indicate the maximum and minimum values. The median is depicted with a solid line (n = 15–25 from at least three independent experiments). Cells were mated at 23°C. Unless indicated, strains with identical genotypes were mated to each other.