1. Mapping Thymine Dimer Splitting in Damaged DNA by Photolyase Zheyun Liu, Chuang Tan, Jiang Li, Xunmin Guo, Lijuan Wang and Dongping Zhong Department of Physics, Chemistry, and Biochemistry, The Ohio State University, Columbus

2. http://www.caribvoice.org/health.html Most photodamage of DNA occurred as cyclobutane pyrimidine dimer. Overexposure of UVA and UVB light will cause the DNA damage, which may induce skin neoplasm. Introduction: DNA damage

3. CPD photolyase specifically repairs cyclobutane pyrimidine dimer Chem. Rev., 103, 2203 (2003)

4. Ultrafast time-resolved spectroscopy Pump-Probe method: One laser pulse initiates the reaction and sets the time zero. (Pump laser) Second laser pulse delays in time and takes the signal at each time delay. (Probe laser)

5. Detecting the weak signals of intermediates The key of differentiate signal of state 2 from total signal is to determine the signal of state 1 first !

6. Charge separation (k 1 ) occurs in 170 ps. Charge recombination (k 2 ) occurs in 560 ps. Flavin retains same redox state during the photocycle. Proc. Natl. Acad. Sci. USA 102, 16128 (2005) How to monitor the evolution of CPD substrate with the injection of one electron? How to measure the dynamics of each elementary steps in reaction?

7. Dissect the DNA repair reaction into elementary steps 70 ps 520 ps

8. Capturing DNA intermediates and products in UV probe-range T-T - T -T - T

9. The absorption coefficients of intermediates and products

10. FET: 170 ps SP1: <10 ps SP2: 70 ps BET: >1500 ps ER: 520 ps FET: forward electron transfer; SP1, splitting of C5-C5’ bond of CPD dimer; SP2, splitting of C6-C6’ bond of CPD dimer; BET: back electron transfer from unpaired CPD; ER: back electron transfer from repaired thymine monomer. The photocycle of CPD repair by photolyase

11. Acknowledgement Dr. Dongping Zhong Lijuan Wang Chuang Tan, Dr. Jiang Li, Dr. Xunmin Guo, and Dr. Ya-Ting Kao All other group members Funding: NIH, Packard Foundation Fellowship Thank you!