Ag. Tkachenko et al., THE ROLE OF PUTRESCINE POTASSIUM ANTIPORT IN ADAPTATION OF ESCHERICHIA-COLI TO AMMONIUM STARVATION/, Microbiology, 65(6), 1996, pp. 644-648
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.