FIGURE 1.

Pik1 is required for proper pheromone signaling. A, Three yeast MAP kinase pathways respond to different stimuli and regulate distinct biological processes, yet all three pathways share signaling components. The MAP kinase kinase kinase (MAPKKK) Ste11 and the adapter Ste50 regulate all three pathways. Some pathway components are not shown for the sake of clarity. MAPKKKK, MAP kinase kinase kinase kinase. B, TetO₇-PIK1 cells were transformed with the FUS1-lacZ transcription reporter and pRS315-PIK1 (pPIK1) or pRS315 (Vector) and treated with α factor pheromone at the indicated concentration for 90 min. β-galactosidase activity was measured spectrofluorometrically. The inset shows activity in cells not stimulated with α factor. Dox, doxycycline; RFU, relative fluorescence units. C, TetO₇-STT4 cells were transformed with the FUS1-lacZ reporter and pRS315-STT4 (pSTT4) or empty vector and treated with α factor pheromone. Results are the mean ± S.E. for three individual experiments each performed in triplicate.