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

Abstract

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 T ₄ DNA (6.3 × 10 ⁻⁴ breaks/2.5 × 10 ⁹ daltons/Jm ⁻² ) and the polA strain (4 × 10 ⁻⁴ breaks/2.5 × 10 ⁹ daltons/Jm ⁻² ), simultaneous induction and repair of breaks were observed in the uvrA, recA and repair proficient strains at doses 4 Jm ⁻² . The final rates of induction in these strains were 1 × 10 ⁻⁴ , 7.5 × 10 ⁻⁵ and 7.5 × 10 ⁻⁵ breaks/2.5 × 10 ⁹ daltons/Jm ⁻² , respectively. A highly efficient polA -dependent repair occurring at 0°C in minimal buffer and a second slower type of repair occurring at 31°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 pol4 (1.6 × 10 ⁻⁴ breaks/2.5 × 10 ⁹ daltons/Jm ⁻² ) and the repair proficient (3.6 × 10 ⁻⁵ breaks/2.5 × 10 ⁹ daltons/Jm ⁻² ) strains, indicate oxygen-enhanced DNA breakage by 313 nm radiation.