Identifying interaction motifs in CK2β -: a ubiquitous kinase regulatory subunit

Casein kinase 2 (CK2) is probably the most ubiquitous serine/threonine kinase found in eukaryotes: it phosphorylates > 300 cellular proteins, ranging from transcription factors to proteins involved in chromatin structure and cell division. CK2 is a heterotetrameric enzyme that induces neoplastic growth when overexpressed. The beta subunit of CK2 (CK2 beta) functions as the regulator of the catalytic CK2 alpha and CK2 alpha' subunits, enhancing their stability, activity and specificity. However, CK2 beta also functions as a multisubstrate docking platform for several other binding partners. Here, we discuss the organization and roles of interaction motifs of CUP, postulate new protein-interaction sites and map these to the known interaction motifs, and show how the resulting complexity of interactions mediated by CK2 beta gives rise to the versatile functions of this pleiotropic protein kinase.