Essential serine/threonine-protein kinase that regulates diverse cellular growth and survival processes including Wnt signaling, DNA repair and circadian rhythms (By similarity). Casein kinases are operationally defined by their preferential utilization of acidic proteins (By similarity). Positively regulates the expression of components of the heterochronic pathway, which regulate developmental timing, such as the transcriptional repressor lin-42 and microRNAs such as let-7 (PubMed:29880558). Negatively regulates cell cycle exit and cell fusion to prevent the premature differentiation of hypodermal seam cells into adult cells (PubMed:15691769). Plays a role in regulating axon branching and subsequently, the maturation of the nervous system, most likely by preventing the premature termination of transcripts for proteins such as Ankyrin/unc-44, which are required for maintaining the nervous system (PubMed:31910362). May phosphorylate ssup-72 to promote nervous system maturation (Probable). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Exhibits substrate-dependent heparin activation. Monomer. Localizes to the nucleus of all cell types and to adherens junctions in the spermatheca. Expressed throughout larval development and into the adult stage in both hypodermal seam cells and the hermaphrodite specific neuron. Constant expression throughout development (PubMed:15691769, PubMed:29880558). However, expression decreases prior to the L2 larval stage, increases at the beginning of the L3 larval stage, and then decreases and plateaus from the mid L3 larval stage onwards (PubMed:31910362, PubMed:29880558). In the nervous system, expressed as dim speckles in developing DD motor neurons from the 3-fold stage of embryogenesis, then expression is dim in neurons of L1 stage larvae (PubMed:31910362). At the L2 larval stage, it is highly expressed in epidermal cells and motor neurons (PubMed:31910362). At the L4 laravl stage, it is expressed in all cell types and in the spermatheca (PubMed:31910362). Expressed throughout development. Highly expressed throughout development. Highly expressed throughout development. Weakly expressed throughout development. Expressed throughout development. Weakly expressed throughout development. RNAi-mediated knockdown results in precocious seam cell fusion and the early exit of seam cell from the cell cycle during the L4 larval stage (PubMed:15691769). RNAi-mediated knockdown does not impair alae formation (PubMed:15691769). RNAi-mediated knockdown results in a squat body statue, referred to as a dumpy phenotype, and rescues the incomplete alae formation defect in the lin-42 (n1089) mutant (PubMed:29880558). RNAi-mediated knockdown increases the survival rate and partially restores alae formation of let-7 n2853 mutants at 20 dgrees Celsius (PubMed:15691769). RNAi-mediated knockdown rescues the lethal bursting phenotype that occurs after the L4 stage molt in the let-7(n2853) mutant at 25 degrees Celsius (PubMed:29880558). Belongs to the protein kinase superfamily. CK1 Ser/Thr protein kinase family. Casein kinase I subfamily.