(a) Rag acts through TORC1 to regulate S6K phosphorylation. HEK293 cells were transfected with constructs as indicated. Co-expression of of mTORKD construct (600 ng) or rapamycin treatment (rapa, 20 nM, 30 min) abolished the effect of RagAQ66L and RagCS75N on S6K phosphorylation. The protein level of mTORKD was determined by immunoblotting with anti-mTOR antibody. 