Poster abstracts

Poster number 47 submitted by Yu Kay Law

Structural Origin of the Sequence Dependence of Thymine Dimer Formation

Yu Kay Law (Biophysics Program, The Ohio State University), Robert A. Forties (Department of Physics, The Ohio State University), Xin Liu (Department of Chemistry, The Ohio State University), Michael G. Poirier (Department of Physics and Biophysics Program, The Ohio State University), Bern Kohler (Department of Chemistry and Biophysics Program, The Ohio State University)

Abstract:
The cyclobutane pyrimidine dimer (CPD) is the most prevalent mutagenic photolesion in UV-irradiated DNA (1, 2). Many studies have established that CPD yields depend sensitively on base sequence (3), but the underlying factors responsible for this sensitivity are unclear. We have determined CPD formation kinetics and yields following UVC irradiation of a 247 bp oligonucleotide containing Cy3 and Cy5 fluorescent end labels. Following UV irradiation, the DNA was digested with T4 pyrimidine dimer glycosylase and the resulting fragments were separated by polyacrylamide gel electrophoresis and detected by fluorescence imaging. The results show that thymine CPD formation yields are attenuated by the presence of a purine base at the 5’ end. In addition, thymine CPD formation yields are reduced when the 3’-flanking base is guanine or cytosine compared to when the 3’-flanking base is adenine or thymine. From the experimentally measured yields, we have constructed a simple model for predicting thymine dimer yields in naked DNA for any of the 9 possible sequence contexts in which the flanking bases adjacent to the TT step are A, G, or C. In addition to giving satisfactory agreement with our experimental results, the model predicts relative CPD formation yields in good agreement with results from other studies.

References:
1. Douki, T., A. Reynaud-Angelin, J. Cadet, and E. Sage. 2003. Bipyrimidine Photoproducts Rather than Oxidative Lesions Are the Main Type of DNA Damage Involved in the Genotoxic Effect of Solar UVA Radiation. Biochemistry 42:9221-9226.
2. Mouret, S., C. Baudouin, M. Charveron, A. Favier, J. Cadet, and T. Douki. 2006. Cyclobutane pyrimidine dimers are predominant DNA lesions in whole human skin exposed to UVA radiation. Proc. Natl. Acad. Sci. USA 103:13765-13770.
3. Brash, D. E., and W. A. Haseltine. 1982. UV-induced mutation hotspots occur at DNA damage hotspots. Nature 298:189-192.

Keywords: UV damage, pyrimidine dimer, DNA sequence