Mechanism of Sensitization to UV Radiation by 5‐Br‐Uracil Substituted DNA

Abstract

DNA, in which thymine is substituted by 5-bromouracil is sensitized to the effect of ultraviolet light. Various chemical changes produced in the DNA are described. These include single and double strand breaks, base loss, protein DNA crosslinks as well as the influence of the three dimensional structure of DNA on some of these changes.The biological system dealt with here is a bacteriophage called T3 which grows on E. coli as host. It has a DNA of approximately 23 x lo6 daltons, which is surrounded by a protein coat. Up to 85% of the thymine in this phage DNA can be substituted by 5-bromouracil (BU) and the viability of the resulting phage particles is very little affected by this.

The Lesions Produced by Ultraviolet Light in DNA Containing 5-Bromouracil

“…Hewitt's results would indicate that only one-fifth of the breaks observed in alkali actually exist in neutral. However, as described in the next section, the measured number of double-strand breaks in two sets of experiments (Lion, 19706;Smets & Cornelis, 1971) is that which would be expected if essentially all the single-strand breaks determined in alkali also existed in neutral solution. Furthermore, in bacterial transformation a DNA single-strand break measured in alkali has the same effect as a break introduced by the enzyme deoxyribonuclease I (Hutchinson & Hales, 1970), as described in the section of this review on bacterial transformation.…”

Formation of ssb, dsb, and Uracil in Monofilarly and Bifilarly Bromouracil-Substituted DNA Molecules

“…In several earlier investigations the mechanism of ssb induction was examined [5 -9] and dsb in duction was shown [5,[9][10][11][12],…”