InterPro domain: IPR000704

Casein kinase, a ubiquitous well-conserved protein kinase involved in cell metabolism and differentiation, is characterised by its preference for Ser or Thr in acidic stretches of amino acids. The enzyme is a tetramer of 2 alpha- and 2 beta-subunits [ 1 , 2 ]. However, some species (e.g., mammals) possess 2 related forms of the alpha-subunit (alpha and alpha'), while others (e.g., fungi) possess 2 related beta-subunits (beta and beta') [ 3 ].

The alpha-subunit is the catalytic unit and contains regions characteristic of serine/threonine protein kinases. The beta-subunit is believed to be regulatory, possessing an N-terminal auto-phosphorylation site, an internal acidic domain, and a potential metal-binding motif [ 4 ]. The beta subunit contains, in its central section, a cysteine-rich motif, CX(n)C, that could be involved in binding a metal such as zinc [ 4 ]. The mammalian beta-subunit gene promoter shares common features with those of other mammalian protein kinases and is closely related to the promoter of the regulatory subunit of cAMP-dependent protein kinase [ 5 ].

1. Human phosvitin/casein kinase type II. Molecular cloning and sequencing of full-length cDNA encoding subunit beta. Eur. J. Biochem. 183, 227-33
2. Structure of the gene encoding human casein kinase II subunit beta. J. Biol. Chem. 266, 13706-11
3. Cloning and disruption of CKB1, the gene encoding the 38-kDa beta subunit of Saccharomyces cerevisiae casein kinase II (CKII). Deletion of CKII regulatory subunits elicits a salt-sensitive phenotype. J. Biol. Chem. 270, 10395-404
4. Cloning and disruption of CKB2, the gene encoding the 32-kDa regulatory beta'-subunit of Saccharomyces cerevisiae casein kinase II. J. Biol. Chem. 269, 18192-200