Protein kinase CK2 (also known as casein kinase 2) has catalytic (α, α′) and regulatory (β) subunits. The role of carboxyl amino acids in positions from 324 to 328 was studied for Xenopus laevis CK2α. Deletions and mutations of these residues were produced in recombinant CK2α, which was assayed for kinase activity. Activity dropped 7000-fold upon deletion of amino acids 324–328. The key residues are isoleucine 327 and phenylalanine 324. A three dimensional model of CK2α indicates that these hydrophobic residues of helix αN may interact with hydrophobic residues in helix αE which is linked to the catalytic center.
