Effect of ultraviolet radiation on the Bacillus subtilis phages SPO2, SPP1 and φ29 and their DNAs

A comparative study of the effects of ultraviolet radiation on three Bacillus subtilis phages is presented. Phages φ29, SPP1 and SPO2c12 or their DNAs were irradiated by UVC (254 nm) and quantum yields for inactivation were calculated. For each phage, the purified DNA was found to be more sensitive than the intact virus when assayed in a uvr⁺ host. The data imply that this is because transfecting DNA is repaired less efficiently than DNA of the intact phage; rather than because of differences in sensitivity to lesion production. Even though φ29 has the smallest target size of the three phages, φ29 and its DNA are the most sensitive. Phages SPO2 and SPP1 code for gene products which complement the repair system of the host. The transfecting DNA of phage SPP1 is extremely sensitive to UV damage when assayed in a uvr⁻ host. This is attributed to the fact that in transfection SPP1 DNA must undergo recombination for productive infection to occur. The recombination process strongly interferes with the repair damaged DNA.