THE ROLE OF PUTRESCINE POTASSIUM ANTIPORT IN ADAPTATION OF ESCHERICHIA-COLI TO AMMONIUM STARVATION/

Ammonium depletion in the nutrient medium induced an active transport of putrescine into the cell, which was not associated with its utiliza tion as a nitrogen source. The uptake of putrescine was accompanied by a proportional release of potassium from the cells. Quantitative anal ysis of free as well as weakly and tightly bound pools of putrescine s howed that this diamine was bound mainly to DNA. Topological studies b y the plasmid method indicated an increase in DNA supercoiling in resp onse to putrescine transport. In vitro experiments made it possible to establish an ambiguous dependence of DNA topology on putrescine conte nt--its physiological concentrations (0.5-1.0 mM) enhanced DNA superco iling, while higher concentrations (2-10 mM) caused gradual relaxation of DNA. A possible physiological significance of these effects in ada ptive response of cells to ammonium deficiency is discussed.