Involved in circadian rhythms, viability and molecular oscillations of the clock genes period (per) and timeless (tim). Dbt reduces the stability and thus the accumulation of monomeric per proteins, probably through phosphorylation. No evident circadian oscillation is detected in head. Together with CkIalpha, regulates processing of ci by phosphorylating it which promotes its binding to slmb, the F-box recognition component of the SCF(slmb) E3 ubiquitin-protein ligase (PubMed:16326393). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Forms a complex with per (PubMed:9674431). Interacts with Dlish (PubMed:27692068). Expressed in photoreceptor cells of the eyes as well as in the region situated between the optic lobe and the central brain. Belongs to the protein kinase superfamily. CK1 Ser/Thr protein kinase family. Casein kinase I subfamily.