Catalytic subunit of a constitutively active serine/threonine-protein kinase complex that phosphorylates a large number of substrates containing acidic residues C-terminal to the phosphorylated serine or threonine (By similarity). Phosphorylates YTA7 during S-phase to promote transcription of histones (PubMed:22156209). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Tetramer composed of an alpha chain, an alpha', one beta chain and one beta' chain (PubMed:12242279). Interacts with FACT subunits POB3 and SPT16 (PubMed:12242279). Interacts with NAP1 (PubMed:18086883). Interacts with YTA7 (PubMed:22156209). Present with 4540 molecules/cell in log phase SD medium. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family. CK2 subfamily.