Tetramer composed of an alpha subunit, an alpha' subunit and two beta subunits. Interacts with CD163 and TCTEX1D3. Also component of a CK2-SPT16-SSRP1 complex composed of SSRP1, SUPT16H, CSNK2A1, CSNK2A2 and CSNK2B, the complex associating following UV irradiation.