Activator of yeast transcription factor, STE12. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] ATP + L-tyrosyl-[protein] = ADP + H(+) + O-phospho-L-tyrosyl-[protein] A number of isoforms are produced. According to EST sequences. Belongs to the protein kinase superfamily. CMGC Ser/Thr protein kinase family. Lammer subfamily.