(a) RagAQ66L and RagCS75N activate TORC1 in the absence of amino acids. Each Rag construct (200 ng) indicated was co-transfected with HA-S6K (20 ng) into HEK293 cells. Cells were starved of amino acids for 1 h before collection. Phosphorylation and protein levels were determined by immunoblotting with the appropriate antibodies, as indicated. 