Pheromone diffusion halo assay identifies amino acids responsible for reduced efficiency of a-factor processing by AtICMTA. Growth inhibition halos produced by a-factor secretion on a mat of sst2α cells. A, Wild-type Ste14 cells. B to G, ste14Δ mutants cells expressing: AtICMTA (B), AtICMTB (C), AticmtAmR154R155E165Q187R188 (D), AtICMTB (E), AticmtAmR154R155E165Q187R188 (F), and vector control (G). B, C, D, and G cells were transformed with 2μ high-copy-number plasmids. E and F cells were transformed with CEN single-copy plasmids.