MAP4K component of the MAPK pathway required for the mating pheromone response. Phosphorylates histone H2B to form H2BS10ph (By similarity). Phosphorylates tea1. Required for skb1-dependent mitotic inhibitory function. Regulates microtubule dynamics and cell polarity. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Forms an activated complex with GTP-bound ras-like cdc42. Interacts with skb1 and the SH3 domain of skb5 via its amino-terminal regulatory domain. Skb1, cdc42 and shk1 are able to form a ternary complex in vivo. Interacts with rga8 and may interact with byr2. Localizes at cell ends, septum forming regions and at the mitotic spindle. Autophosphorylated on serine residues. Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. STE20 subfamily.