FIG 1.

Experimental design. E. coli strain MG1655-SILAC was grown in medium containing heavy-labeled arginine and lysine to mid-log phase, followed by a chase with a 20-fold excess of unlabeled (light) arginine and lysine, and grown for 2 weeks to obtain stationary-phase cells. Samples were collected at the indicated time points and divided into three aliquots. Then, ribosomes were isolated using sucrose gradient centrifugation (A), the RNA quantity was determined by hot-phenol extraction (B), the r-protein quantity was determined using LC-MS/MS (C), and the r-protein stoichiometry in the total proteome was ascertained using LC-MS/MS (D).