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 (bio-logical 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 in-duction of breaks was linear in purified T4DNA (6.3 x 10 " 4 breaks/2.5 x 109 daltons/Jm- *) and the polA strain (4 x 10 " 4 breaks/2.5 x 109 daltons/Jm ~ *), simultaneous in-duction and repair of breaks were observed in the uvrA, recA and repair proficient strains at doses <5 x 104 Jm~2. The final rates of induction in these strains were l x l O ~ 4, 7.5 x 10- 5 and 7.5 x 10~5 breaks/2.5 x 109 daltons/Jm-2, respectively. A highly efficient /?o£4-dependent repair occurr-ing at 0°C in minimal buffer and a second slower type of repair occurring at 31°C in the polA strain were detected. Ox-ygen 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 109 daltons/Jm-2) and the repair proficient ( 3. 6 x l 0 ~ 5 breaks/2.5 x 109 daltons/Jm " ̂ strains, indicate oxygen-enhanced DNA breakage by 313 nm radiation