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Fate of Thymine-containing Dimers in the Deoxyribonucleic Acid of Ultraviolet-irradiated Bacillus subtilis

^a Radiobiology Laboratories, School of Medicine, Yale University, New Haven, Connecticut

ABSTRACT

The fate of ultraviolet-induced, thymine-containing dimers in the deoxyribonucleic acid (DNA) of Bacillus subtilis was investigated in both the wild type (UV^R) and an ultraviolet light-sensitive (UV^S) mutant. During incubation in the dark, dimers were excised from the DNA of the UV^RB. subtilis, but remained in the DNA of the UV^S mutant. About 40% of the excised dimers recovered in the wild type were in the acid-soluble fraction; the remainder were in the incubation medium. A UV^S mutant of Escherichia coli K-12, shown previously to be defective in dimer excision, was irradiated with ultraviolet light and incubated under visible light for 3 hr. About 65% of thymine-containing photoproducts were removed from the DNA. These photoproducts were not recovered in the acid-soluble fraction. In comparison, the UV^S mutant of B. subtilis lost only 13% of such photoproducts from DNA when exposed to light under the same conditions.

¹ Present address: National Institute of Arthritis and Metabolic Diseases, Bethesda, Md.