Phleomycin-Stimulated Degradation of Deoxyribonucleic Acid in Escherichia coli

Abstract

Phleomycin stimulates the degradation of DNA by energy-dependent endonuclease and exonuclease reactions in Escherichia coli rec + cells and in recB − and recC − cells that lack an adenosine triphosphate-dependent nuclease functioning in the repair of ultraviolet (UV) lesions. Exonuclease activity is blocked in T4 phage-infected cells. The endonuclease reaction produces 10 7 -dalton segments resembling those produced in colicin E2-treated cells. These differ from the random-sized segments produced in UV-irradiated cells, or the 10 6 -dalton segments made in T4 phage-infected cells. A mutant selected for phleomycin tolerance is cross-tolerant to colicin E2, and some mutants selected for colicin E2 tolerance are cross-tolerant to phleomycin. On the basis of these cross-tolerances and the similarities between the effects of phleomycin and E2-stimulated nucleases, the suggestion is made that both agents may stimulate the same nuclease reactions in E. coli cells.