(b) RagAT21N and RagCQ120L block S6K phosphorylation in response to amino acid (AA) stimulation. pcDNA3 (200 ng, lanes 1 and 2) or each indicated Rag construct was co-transfected with HA-S6K into HEK293 cells. Cells were starved of amino acids for 1 h (-AA) and either remained in the starvation medium or were stimulated with amino-acid-containing-medium (+AA) for 30 min before collection. Phosphorylation and protein levels were determined by immunoblotting with the appropriate antibodies, as indicated. 