Casein kinases are operationally defined by their preferential utilization of acidic proteins such as caseins as substrates. The alpha chain contains the catalytic site. May participate in Wnt signaling. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Tetramer of two alpha and two beta chains. RNAi-mediated knockdown results in mislocalization of mbm in interphase cells with partial localization to the cytoplasm as well as nucleolar expression. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. CK2 subfamily.