Regulation of the synthesis of ribonucleoside diphosphate reductase in Escherichia coli: specific activity of the enzyme in relationship to perturbations of DNA replication.

Ribonucleoside diphosphate reductase (RDP reductase) activity was found to greatly increase after a shift to the nonpermissive temperature in Escherichia coli mutants temperature sensitive for DNA elongation (dnaE dnaG dnaZ lig) or DNA initiation (dnaA dnaC dnaI). However, the kinetics of increase in RDP reductase after a shift to nonpermissive conditions were significantly different in initiation-defective mutants compared with elongation-defective mutants. In strains without defects in DNA metabolism, the specific activity of RDP reductase was found to increase with increasing growth rate. Nutritional shifts to faster growth conditions caused cells to transiently overproduce RDP reductase before adjusting to the new steady-state conditions.