Expression of mTOR Q2223K led to stronger S6K phosphorylation than that of wild-type mTOR (figure 2a), and the observed hyperactivation persisted over lower serum concentrations (figure 2b, supplementary figure S5). Q2223K mutant mTOR was equally sensitive to rapamycin and its analogues as wild-type mTOR (figure 2c, supplementary figure S6). Upon co-transfection of exogenous S6K, a process known to augment mTORC1 signaling, we observed further increase in the hyperactivity of mTOR Q2223K with preserved rapamycin sensitivity (figures 2d, 2e).