Serine/threonine protein kinase involved in conjugation and sporulation (PubMed:2046669, PubMed:1435723). It is thought that it phosphorylates the byr1 protein kinase which itself phosphorylate the spk1 kinase (PubMed:2046669, PubMed:1435723). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with rad24 and rad25; these prevent its translocation to the cell membrane during nitrogen starvation. Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. MAP kinase kinase kinase subfamily.