Casein kinases are operationally defined by their preferential utilization of acidic proteins such as caseins as substrates. It can phosphorylate a large number of proteins (By similarity). Phosphorylates tubulins and microtubules in vitro (PubMed:18945931). Involved in anisotropic cell growth and cell shape formation via the regulation of microtubule organization (PubMed:18945931, PubMed:19820321). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Monomer (By similarity). Binds tubulins (PubMed:18945931). Present in punctate particles with granular structure (PubMed:16126836, PubMed:18945931, PubMed:19820321, PubMed:19941015). Associates transiently with cortical microtubules. Shuttles between microtubules and punctate particles in a kinase activity-dependent manner (PubMed:18945931, PubMed:19820321). Localizes to motile vesicle-like structures (late endosomal-like compartments) found both in the cytoplasm and at the cell periphery, especially at the cellular junctions (PubMed:19941015). Autophosphorylated. Abnormal cortical microtubule organization leading to anisotropic cell expansion. Belongs to the protein kinase superfamily. CK1 Ser/Thr protein kinase family. Casein kinase I subfamily. Truncated N-terminus.