THE ROLE OF PUTRESCINE AND POTASSIUM-TRANSPORT IN THE REGULATION OF DNA TOPOLOGY DURING ESCHERICHIA-COLI ADAPTATION TO HEAT-STRESS

The effect of a temperature increase to 52 degrees C or the addition o f ethanol (6%) to an exponential Escherichia coli culture on putrescin e and potassium transport was studied, The first stage of heat shock w as accompanied by a decrease in the extent of DNA supercoiling, due to the dissociation of the putrescine-DNA complex. The loss of potassium ions at this phase produced a synergistic effect. The second phase of the heat shock was characterized by a reversal. in the direction of p utrescine and potassium transport, which was accompanied by the restor ation of the prestress extent of DNA supercoiling. An increase in the ATP pool and cell energy charge resulting from the uncoupling of the e nergy metabolism and synthetic processes also played an important role in the restoration of the initial DNA topology at the second phase of the heat shock via the activation of the energy-dependent gyrase or t he heat shock protein DnaK. A mechanism is suggested that explains the involvement of putrescine in the regulation of DNA topology, which is a universal regulator of gene expression under stress, heat shock in particular.