Site-specific effect of thymine dimer formation on dA(n)·dT(n) tract bending and its biological implications

C. I. Wang, J. S. Taylor

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dA(n)·dT(n) sequences, otherwise known as A tracts, are hotspots for cis-syn thymine dimer formation and deletion mutations induced by UV light. Such A tracts are also known to bend DNA, suggesting that some biological effects of UV light might be related to the distinctive structure and properties of cis-syn dimer-containing A tracts. To investigate the effect of thymine dimer formation on A-tract bending multimers of all possible dimer monoadducts of a dA6·dT6-containing decamer known to bend DNA were prepared along with multimers of a dimer-containing 21-mer of heterogeneous sequence. The characteristic anomalous electrophoretic behavior of the phased A-tract multimers was essentially abolished by dimer formation at the center of the A tract and was only slightly reduced by dimer formation at the ends. These effects are attributed to disruption of the A-tract structure at the site of the dimer, resulting in intact A tracts of reduced length and, hence, reduced bending. This model was suggested by the ability to formulate the estimated bend angles of the dimer-containing A tracts as approximately equal to the sum of the bend angles induced by the dimer and the remaining intact portion of the A tract. Contrary to a previous experimental study that concluded that the thymine dimer bends DNA by ≃30°, the dimer was determined to bend DNA by only ≃7°. Reduction of the bending of a DNA sequence by dimer formation may have a number of unpredicted and important biological consequences.

Original languageEnglish
Pages (from-to)9072-9076
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number20
StatePublished - 1991


  • DNA
  • UV light
  • intrinsic bending
  • thymine dimers


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