Serine/threonine protein kinase involved in conjugation and sporulation. It is thought that it is phosphorylated by the byr2 protein kinase and that it can phosphorylate the spk1 kinase. When bound to bob1, is involved in the regulation of sexual differentiation. 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] Interacts with bob1 and spk1. Localizes to the cell tips and septum forming regions. Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. MAP kinase kinase subfamily.