Inactivation of phage T7 by near-ultraviolet radiation plus hydrogen peroxide: DNA-protein crosslinks prevent DNA injection.

A nonlethal concentration of H2O2 (0.05%) greatly enhances near-ultraviolet (NUV) inactivation of phage T7. Simultaneous treatment with H2O2 and NUV reduces the amount of DNA injected into the bacterial host, but not the number of phage adsorbed. Not only were recombination and gene expression of late markers reduced upon treatment of phage T7 with NUV plus H2O2, but also a gradient of recombination resulted, with markers injected first reduced to a lesser extent than those injected last. Double-strand DNA breaks were not detected; however, DNA-protein crosslinks were observed upon NUV plus H2O2 treatment of double-labeled T7. Previous studies demonstrated that single-strand DNA breaks did not account for phage death by NUV plus H2O2. It is concluded that the DNA-protein crosslinks prevent normal injection of T7 phage DNA; such crosslinks may be important lesions in NUV cellular damage.