1-NA-PP1 is a reversible, cell-permeable inhibitor of Src-family tyrosine kinases that have been mutated, by a single base substitution, to become ‘analog sensitive’ (as), as compared to the wild-type kinase. 1-NA-PP1 was first developed to optimally inhibit v-Src-as1, with an I338G substitution, preferentially over v-Src (IC50 = 1.5 nM versus 1.0 μM, respectively). The homologous mutation in other kinases generated similar analog sensitivity (e.g., IC50 = 1.5 nM for c-Fyn-as1 versus 0.6 μM for c-Fyn; 7.0 nM for c-Abl-as2 versus 0.6 μM for c-Abl; 15 nM for Cdk2-as1 versus 18 μM for Cdk2). This approach has been used to elucidate functions of several kinases in both mammalian and yeast systems.