Cell cycle analysis of leucine uptake (and protein synthesis) during the division cycle. A100-ml amount of E. coli B/r lys mutant cells in culture medium (108 cells per ml growing in minimal medium with glycerol and lysine) was labeled for 2 min with 2 uCi of [14C]leucine (450 mCi/mmol; New England Nuclear Corp.). The cells were then filtered, washed, and analyzed by assaying the radioactivity per cell eluted from the membrane-elution apparatus. The dashed line is the expected pattern for a constant rate of leucine uptake and protein synthesis during the division cycle. This constant rate is predicted by a model of linear rate of increase in mass during the division cycle. The upper cell elution curve has oscillations that are due to the initial cell age distribution of the cells at the time they were filtered. The decrease in the dashed line is placed at the end of the first division cycle as indicated by the cell elution curve. The decreasing exponential curve of radioactivity per cell indicates exponential growth.