Involved in the asymmetric cell division of the embryo downstream of par-2 and par-3 by regulating the asymmetric cortical distribution of pkk-1, a phosphatidylinositol 4,5-bisphosphate-producing enzyme, which in turn regulates the asymmetrical distribution of grp-1, grp-2 and lin-5. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Cortical localization during all cell cycle stages. In the cytoplasm, forms punctate structures around the asters during mitosis. Enriched in the anterior region of the 1 cell-stage embryo. RNAi-mediated knockdown in 1-cell embryos results in mislocalization of the pronuclei and the spindle towards the anterior part of the embryo, spindle instability, and failure of asymmetric cell division in 50 percent of embryos. In addition, spindle pulling forces are increased. par-2 and par-3 mediated embryo polarity is normal. Oocytes have increased cortical grp-1 and grp-2 localization. Belongs to the protein kinase superfamily. CK1 Ser/Thr protein kinase family. Casein kinase I subfamily.