To reveal the mechanism of mTOR complex 1 (mTORC1) in arginine deprivation-based therapy, Wang et al.39 showed that SLC38A9, an amino-acid transporter, signaled arginine sufficiency to mTORC1 and promoted mTORC1-mediated protein synthesis, indicating that blocking this signal could enhance the anti-tumor efficacy of amino-acid depletion enzyme. The gene discussed is SLC38A7; the disease is neoplasm.