Damage by Solar Radiation at Defined Wavelengths. Involvement of Inducible Repair Systems

The susceptibility of bacteriophage damaged by solar‐ultraviolet (UV, 290‐380 nm) radiations at denned wavelengths and by radiation at a visible wavelength (405 nm) to the Weigle reactivation system induced by far‐UV (254 nm) irradiation of the host cell has been studied in a repair competent strain of Escherichia coli. The sector of inducible repair diminishes with wavelength, being very small after 313 nm irradiation and absent after irradiation at longer wavelengths. However, irradiation of bacteria at wavelengths as long as 313 nm induces a bacteriophage reactivation system as effectively as radiation at 254 nm in both the repair competent and an excision deficient host cell. At longer wavelengths pre‐irradiation of the repair competent host cell enhances reactivation of 254 nm irradiated bacteriophage but the reactivation is smaller and the process quite distinct from that induced in the 254‐313 nm region. We conclude that, with increasing wavelength, damage induced by solar UV radiations becomes increasingly less susceptible to repair systems induced by far‐UV (pyrimidine dimers) and that this type of inducible repair system is no longer induced by wavelengths longer than 313 nm.