THE WAVELENGTH-DEPENDENT FRACTION OF BIOLOGICAL DAMAGE DUE TO THYMINE DIMERS AND TO OTHER TYPES OF LESION IN ULTRAVIOLET-IRRADIATED DNA

Abstract— The sensitivity of Hemophilus influenzae transforming DNA to monochromatic ultraviolet radiation has been determined with and without maximum photoreactivation. The fraction of ultraviolet damage which is photoreactivable (the photoreactivable sector) is large and varies with the wavelengths of the inactivating radiation, decreasing at the extremes of the ultraviolet spectrum. Equating photoreactivable damage with thymine dimer damage, we may interpret the wavelength dependence of photoreactivability and the spectrum for non-photo-reactivable damage in terms of the absorption spectra of thymidine and cytosine deoxyriboside. The data suggest that cytosine deoxyriboside alteration is important in non-photoreactivable biological damage.