Fig. 3. DLG1 mutated at Ser158 and Ser442 cannot be phosphorylated by the CDKs. (A,B) GST-tagged Ser158A, Ser442A and the double mutant in which both serines are mutated to alanine were subjected to in vitro kinase assays with CDK1 and CDK2, and analysed by SDS PAGE and autoradiography (upper panels). The lower panels show the Coomassie-blue-stained gels and confirm equal amounts of protein loading. Phosphorylation by both kinases is lost in the mutant lacking both serines.