Induction of oxygen-dependent lethal damage by monochromatic UVB (313 nm) radiation: strand breakage, repair and cell death.

The action of 313 nm radiation in cellular inactivation (biological measurements) and induction and repair of DNA strand breaks (physical measurements) were studied in a repair proficient strain and three repair deficient strains (polA, recA, uvrA) of Escherichia coli K-12. Although the induction of breaks was linear in purified T4DNA (6.3 X 10(-4) breaks/2.5 X 10(9) daltons/Jm-2) and the polA strain (4 X 10(-4) breaks/2.5 X 10(9) daltons/Jm-2), simultaneous induction and repair of breaks were observed in the uvrA, recA and repair proficient strains at doses less than 5 X 10(4) Jm-2. The final rates of induction in these strains were 1 X 10(-4), 7.5 X 10(-5) and 7.5 X 10(-5) breaks/2.5 X 10(9) daltons/Jm-2, respectively. A highly efficient polA-dependent repair occurring at 0 degree C in minimal buffer and a second slower type of repair occurring at 31 degrees C in the polA strain were detected. Oxygen dependence of cellular inactivation was observed for the polA and repair proficient strains irradiated at 313 nm thus providing biological evidence for an oxygen-dependent lesion involved in lethality in the short wavelength range of the solar u.v. The lower hypoxic break induction rates of the polA (1.6 X 10(-4) breaks/2.5 X 10(9) daltons/Jm-2) and the repair proficient (3.6 X 10(-5) breaks/2.5 X 10(9) daltons/Jm-2) strains, indicate oxygen-enhanced DNA breakage by 313 nm radiation.