Pkn5 and pkn6 may have reciprocal roles in growth and development. Pkn5 may be a kinase that negatively regulates development. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Expressed constitutively throughout the life cycle, with slight increases at an early stage of development. Autophosphorylated on serine residues. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.