Reports that STE7 is a dual-specificity kinase that modifies FUS3 at the appropriate sites and stimulates its catalytic activity in vitro. Argument that STE7 is the physiological activator of FUS3; Purification of FUS3 kinase from E. coli and its autocatalytic properties; Pheromone-stimulated haploid yeast cells; MAP kinase activators; Details of the study.