May act as a polo kinase kinase by mediating phosphorylation of plk1/plx1 and subsequent activation of plk1/plx1 during oocyte maturation. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Homodimer. Autophosphorylates. Phosphorylated by plk1/plx1, suggesting the existence of a feedback loop with plk1/plx1. activation of the protein. Belongs to the protein kinase superfamily. STE Ser/Thr protein kinase family. STE20 subfamily. It is unclear whether it acts as an upstream kinase for polo kinase by mediating phosphorylation of plk1/plx1 or whether it is a downstream target of plk1/plx1.