Ultraviolet action spectra for DNA dimer induction, lethality, and mutagenesis in Escherichia coli, with emphasis on the UVB region

Ultraviolet action spectra were obtained for lethality and mutagenesis (reversion to tryptophan independence) in Escherichia coli WP2s for wavelengths 254-405 nm with detailed analysis in the UVB region. Parallel chemical assay yields of pyrimidine dimers in DNA of E. coli RT4 were determined. lethality, mutagenesis and dimer induction all decreased with increasing wavelength. Between 300 and 320 nm, the mutagenesis action spectrum coincides closely with the absorption spectrum of DNA. The lethality spectrum is closely parallel to the mutagenicity spectrum. A calculation derived from the slope of the UVB spectra reveals that a 10nm shift of the solar UV spectrum to shorter wavelengths would result in a 35% increase in its mutagenic potential. At 325 nm, both biological action spectra show sharp decreases in slope. In addition, above 325 nm the spectra for lethality, mutagenicity and dimer formation diverge sharply; lethalities at these UVA wavelengths were approximately tenfold greater relative to mutagenicity than at shorter wavelengths. The relative yield of dimer formation by 365 nm radiation is intermediate between the yields for lethality and mutagenesis. (author)