EXPERIMENTAL FIGURE 14-4 Phenotypes of yeast sec mutants identified five stages in the secretory pathway. These temperature-sensitive mutants can be grouped into five classes based on the site where newly made secretory proteins (red dots) accumulate when cells are shifted from the permissive temperature to the higher, nonpermissive one. Analysis of double mutants permitted the sequential order of the steps to be determined. See P. Novick et al., 1981, Cell 25:461, and C. A. Kaiser and R. Schekman, 1990, Cell 61:723.