Fig. 4. R131 is important for the ability of PDK1 to phosphorylate S6K1. Wild-type or T412E His-S6K1_1–421 were incubated for 10 min with wild-type or mutant GST–PDK1 and Mg[γ-³²P]ATP. Thereafter, the kinase reactions were subjected to SDS–PAGE. Radioactivity incorporated into the S6K1 protein band was quantitated and expressed as a percentage of the maximal value obtained. The results are representative of two independent experiments.