Protein kinase which phosphorylates serine and threonine residues (PubMed:1495994). Can use casein as a substrate (PubMed:1495994). Phosphorylates elongator complex member ELP1/IKI3 on 'Ser-1198' and 'Ser-1202' which promotes the tRNA modification function of the complex (PubMed:25569479). Associated with repair of damaged DNA and meiosis (PubMed:1887218). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with HRI1 (PubMed:21460040). Interacts with ELP1/IKI3; the interaction leads to ELP1/IKI3 phosphorylation (PubMed:21460040). Present with 10300 molecules/cell in log phase SD medium. Belongs to the protein kinase superfamily. CK1 Ser/Thr protein kinase family. Casein kinase I subfamily.