ABL family tyrosine kinases are tightly regulated by autoinhibition and 
phosphorylation mechanisms. These kinases maintain an inactive conformation 
through intramolecular interactions involving SH3 and SH2 domains. RIN1, a 
downstream effector of RAS, binds to the ABL SH3 and SH2 domains and stimulates 
ABL tyrosine kinase activity. RIN1 binding to the ABL2 kinase resulted in a 
large decrease in Km and a small increase in Vmax toward an ABL consensus 
substrate peptide. The enzyme efficiency (k(cat)/Km) was increased more than 
5-fold by RIN1. In addition, RIN1 strongly enhanced ABL-mediated phosphorylation 
of CRK, PSTPIP1, and DOK1, all established ABL substrates but with unique 
protein structures and distinct target sequences. Importantly RIN1-mediated 
stimulation of ABL kinase activity was independent of activation by SRC-mediated 
phosphorylation. RIN1 increased the kinase activity of both ABL1 and ABL2, and 
this occurred in the presence or absence of ABL regulatory domains outside the 
SH3-SH2-tyrosine kinase domain core. We further demonstrate that a catalytic 
site mutation associated with broad drug resistance, ABL1T315I, remains 
responsive to stimulation by RIN1. These findings are consistent with an 
allosteric kinase activation mechanism by which RIN1 binding promotes a more 
accessible ABL catalytic site through relief of autoinhibition. Direct 
disruption of RIN1 binding may therefore be a useful strategy to suppress the 
activity of normal and oncogenic ABL, including inhibitor-resistant mutants that 
confound current therapeutic strategies. Stimulation through derepression may be 
applicable to many other tyrosine kinases autoinhibited by coupled SH3 and SH2 
domains.