Putrescine as a factor protecting Escherichia coli against oxidative stress

The level of expression of oxyR, the gene that protects Escherichia coli ag ainst oxidative stress, was enhanced by physiological concentrations of the biogenic amine putrescine. This level was directly proportional to the deg ree of negative DNA supercoiling. 1,4-Diamino-2-butanone (DAB), a specific inhibitor of ornithine decarboxylase, the key enzyme of polyamine synthesis , produced an inhibitory effect on the level of oxyR expression under oxida tive stress, which was relieved by the addition of putrescine. The direct r elationship between the putrescine concentration and the degree of negative DNA supercoiling suggests that the mechanism of action of putrescine as th e modulator of oxyR transcription activity is based on both its direct infl uence on the gene expression level and its indirect effect mediated by topo logical DNA changes. Putrescine was shown to produce a protective effect if the DNA is damaged by reactive oxygen species.