Studies on DNA-Dependent RNA Polymerase from Escherichia coli. 1. The Mechanism of Polyamine Induced Stimulation of Enzyme Activity

Abstract

The effect of spermidine and spermine on the synthesis of RNA in vitro by RNA-polymerase from Escherichia coli has been studied. Spermidine did not change the pH optimum of the reaction. With a high ratio of DNA to polymerase in the reaction mixture, maximal stimulation was observed at a spermidine concentration of 0.8 mM and spermine concentration of 0.3 mM. Under these conditions spermidine increased the initial velocity and the extent of the reaction. When the weight ratio of DNA to enzyme was low, the same concentration of spermidine increased the extent, but not the initial velocity of the reaction. If the reaction was primed by denatured DNA, spermidine did not stimulate the synthesis of RNA. A slight inhibition was observed at low concentrations of the template. Spermidine counteracted the inhibitory effect of RNA added to the reaction mixture before the start of the reaction. Models based on these results are proposed to explain the mechanisms of polyamine induced stimulation of RNA polymerase activity.