Casein kinase II phosphorylation site

Casein kinase II (CK-2) is a protein serine/threonine kinase whose activity is independent of cyclic nucleotides and calcium. CK-2 phosphorylates many different proteins. The substrate specificity [1] of this enzyme can be summarized as follows:

 (1) Under comparable conditions Ser is favored over Thr.
 (2) An acidic residue (either Asp or Glu) must be present three residues from
     the C-terminal of the phosphate acceptor site.
 (3) Additional acidic  residues in  positions +1, +2, +4, and +5 increase the
     phosphorylation rate.  Most  physiological  substrates  have at least one
     acidic residue in these positions.
 (4) Asp is preferred to Glu as the provider of acidic determinants.
 (5) A basic residue at the N-terminal  of the  acceptor  site  decreases  the
     phosphorylation rate, while an acidic one will increase it.