Regulatory subunit of casein kinase II/CK2. As part of the kinase complex regulates the basal catalytic activity of the alpha subunit a constitutively active serine/threonine-protein kinase that phosphorylates a large number of substrates containing acidic residues C-terminal to the phosphorylated serine or threonine (By similarity). Participates in Wnt signaling (By similarity). Casein kinase II/CK2 is a tetramer composed of an alpha subunit, an alpha' subunit and two beta subunits. The beta subunit dimerization is mediated by zinc ions. Interacts with CD163. Also component of a CK2-SPT16-SSRP1 complex composed of SSRP1, SUPT16H, CSNK2A1, CSNK2A2 and CSNK2B, the complex associating following UV irradiation (By similarity). Interacts with DYNLT2. Interacts with MUSK; mediates phosphorylation of MUSK by CK2. Interacts with FGF1; this interaction is increased in the presence of FIBP, suggesting a possible cooperative interaction between CSNKB and FIBP in binding to FGF1 (By similarity). Phosphorylated by alpha subunit. The N-terminus is blocked. Belongs to the casein kinase 2 subunit beta family.