Effect of UV Induced DNA Lesions on the Activity of Escherichia Coli DNA Topoisomerases: A Possible Role of these Enzymes in DNA Repair
Modifications of DNA structure by a number of DNA damaging agents cause distortions resulting in the unwinding of the DNA helix. We have shown that the unwinding angle due to the formation of pyrimidine dimers in a circular DNA molecule is very small and inadequate to cause helix disruption. Although the alteration of DNA superhelicity produced by photodimers appeared very limited — at least 25 dimers were necessary in order to unwind a single topoisomer by one superhelical turn (1) — it was enough to affect the activity of Micrococcus luteus DNA topoisomerase I: one dimer per molecule inhibited the activity of this enzyme, by 5% (2).
KeywordsCysteine Electrophoresis Bacillus Manes Pyrimidine
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