Ribosome r-protein content during stationary phase

The aim of this study was to determine the fate of ribosomes and r-proteins. In this respect, SILAC (Stable Isotope Labeled Amino acids in cell Culture) based experimental approach was used (Fig. 1). E.coli cells were grown in MOPS medium supplemented with “heavy” labeled arginine (Arg10) and lysine (Lys8). At the mid-log phase, the culture was further supplemented with a 20-fold molar excess of “light” unlabeled arginine (Arg0) and lysine (Lys0), divided into 8 aliquots, and grown for 14 days. Cell samples were collected at day one (24h), day two (48h), and subsequently in 48h intervals over the following 12 days. The ribosome particles were isolated using sucrose gradient centrifugation. the quantities of r-proteins in the 70S ribosome fraction were determined using SILAC based LC-MS/MS and normalized to the corresponding values of day one.