The rate of differential synthesis of β-galactosidase (αlac) was measured in maximally induced cultures of Escherichia coli B/r with 0.01 M-inducer and 0.01 M-cyclic AMP. The value of αlac decreases with growth rate (60% between 0.67 and 2.1 doublings/h) and after a nutritional shift-up. This decrease is presumed to reflect a decrease in the intracellular concentration of free active RNA polymerase after a shift-up, which implies that the increase in ribosome synthesis after a shift-up is due to an active induction of the ribosomal components.
