Isolation and Properties of YCK2, a Saccharomyces cerevisiae Homolog of Casein Kinase-1

A soluble fragment of YCK2, a casein kinase-1 isoform from Saccharomyces cerevisiae, has been purified and characterized in vitro. The procedure enriches enzyme activity to a final specific activity of 4.7 μmol min−1 mg−1 (when assayed with casein as substrate). Structural analysis reveals that the preparation arises from N-terminal modification and C-terminal proteolysis of the initially synthesized 546-residue protein, consisting of residues 2-495 ± 1. Kinetic analysis demonstrates that YCK2 is similar to casein kinase-1 isolated from other organisms in its inability to use GTP as nucleotide substrate, in its sensitivity to heparin and ribofuranosylbenzimidazole inhibitors, and in its peptide substrate selectivity. The enzyme is unusual, however, in that it is insensitive to the potent mammalian casein kinase-1 inhibitor N-(2-aminoethyl)-5-chloroisoquinoline-8-sulfonamide.