<p>Chk1-mediated phosphorylation of three C-terminal CK1δ fusion protein sets containing either wild-type or mutant sequences encompassing amino acids 305–375 (<b>A</b>), 353–375 (<b>B</b>), and 375–428 (<b>C</b>) of the rat CK1δ sequence. The GST-CK1δ fusion proteins were phosphorylated by Chk1 <i>in vitro</i> and separated in SDS-PAGE. Substrate phosphorylation was quantified by Cherenkov counting. Results are shown as normalized bar graphs.</p
