ESR-Studies of Normal and 5-Bromouracil-Substituted DNA of Bacillus subtilis after Irradiation with Ultraviolet Light

Abstract

Electron spin resonance signals are induced, at 77°K and in the presence of water, in B. subtilis DNA in which about 70% of the thymine has been replaced by 5-bromouracil, either by short wavelength ultraviolet light (UV) (2400-4000 A) or by long wavelength UV (3200-4000 A). In DNA not containing bromouracil, short wavelength UV induces signals; long wavelength UV produces no detectable signal, indicating a rate of production at least ten times lower than in DNA containing bromouracil. Bromouracil in the DNA suppresses the thymine ESR spectrum to a greater extent than the degree of thymine replacement. The signal induced in DNA containing bromouracil is the same with both ultraviolet radiations, a triplet with g = 2.0023 and an overall splitting of 46 G and a superposed singlet, quite different from that for irradiated bromodeoxyuridine, or a nucleoside mixture. It is unchanged by substituting D2 O for H2 O. The probable location of the radical responsible for the triplet is on the sugar. In the presence ...