Polyamines protect against DNA strand breaks and aid cell survival againstirradiation in Escherichia coli

Polyamines protected plasmid DNA strand breaks in vitro and aided the cell survival against irradiation in polyamine-deficient Escherichia coil mutant strain. DNA strand breaks were prevented 4-6 fold more by spermidine and s permine than by putrescine and cadaverine in the dithiothreitol/Fe(III)/O-2 system. After UV-irradiation, the protection of DNA strand breaks by sperm ine and spermidine was twice as effective as that by putrescine and cadaver ine. Survivability of polyamine-deficient Escherichia coil mutant cells gro wn in the medium containing putrescine and spermidine was 2.4- and 3.0-fold as high as in polyamine-depleted medium at a dose of 60 and 40 J/m(2). Aft er gamma-irradiation to a dose of 80 Gy, cell survivals of a mutant strain were significantly increased to 7.7- and 23.8-fold by putrescine and spermi dine, respectively. These results implicate the possibility that polyamines play a potent role in the protection of DNA or cell damage by radiation.