Influence of Salts on RNA Synthesis by DNA‐Dependent RNA‐Polymerase from <i>Escherichia coli</i>

Abstract

The effect of salt concentration on RNA synthesis by DNA‐dependent RNA‐polymerase from Escherichia coli has been investigated. For a double stranded template the following influences are observed: (1) Free enzyme and enzyme bound to DNA, but not synthesizing RNA, are inhibited above an ionic strength of about 0.15. (2) The rate of RNA‐synthesis, by those enzyme molecules which have started RNA chains, is stimulated by increasing the salt concentration up to an optimum. Magnesium salts cause a larger stimulation than monovalent cations. However, the optimal effect always occurs at an ionic strength of about 0.36. (3) This stimulatory effect is distinguished from the cofactor function which requires only low concentrations of divalent cations (Mg 2+ , Co 2+ , Mn 2+ ). (4) RNA synthesis stops at low ionic strength (&lt;0.2) due to a first order inactivation of the synthesizing enzyme. At high ionic strength synthesis continues over many hours at a slowly decreasing rate. Raising the ionic strength after RNA synthesis has stopped at low ionic strength causes an immediate resumption of synthesis. Mg 2+ and spermidine are most effective in this action. However, Co 2+ and Mn 2+ are unable to reactivate the enzyme once it has stopped. With single stranded DNA as template neither a first order inactivation of synthesizing enzyme at low ionic strength nor a stimulation of RNA synthesis by monovalent salts is observed. The effect of divalent cations on enzyme activity can be due to their cofactor function.