Catalytic subunit (alpha) of the Serine/Threonine Kinase, Casein Kinase 2
STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. CK2 is a tetrameric protein with two catalytic (alpha) and two regulatory (beta) subunits. It is constitutively active and ubiquitously expressed, and is found in the cytoplasm, nucleus, as well as in the plasma membrane. It phosphorylates a wide variety of substrates including gylcogen synthase, cell cycle proteins, nuclear proteins (e.g. DNA topoisomerase II), and ion channels (e.g. ENaC), among others. It may be considered a master kinase controlling the activity or lifespan of many other kinases and exerting its effect over cell fate, gene expression, protein synthesis and degradation, and viral infection. CK2 is implicated in every stage of the cell cycle and is required for cell cycle progression. It plays crucial roles in cell differentiation, proliferation, and survival, and is thus implicated in cancer. CK2 is not an oncogene by itself but elevated CK2 levels create an environment that enhances the survival of tumor cells. The CK2 subfamily is part of a larger superfamily that includes the catalytic domains of other STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.
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