Schematic illustration of the method developed by Shokat et al. to identify kinase substrates. Analogue sensitive (As)-kinase contains a mutation in the ATP binding domain that enables it to function with both ATP (A) and a bulky ATP derivative (A*), while wild-type (WT) kinase can only functional with A. Hodgson, D. R.; Schröder, M. Chemical Society Reviews 2011, 40, 1211–1223. Reproduced with permission from The Royal Society of Chemistry.