0 Deoxyribose-N C=0 0 CH3 H -N Deoxyribose-N C=0 H CH3 Two thymine residue UV irradiation 0 c一N Deoxyribose-N H C=0 CH3 ⊙ 0 -N Deoxyribose—N CC=0 H CH3 Thymine-thymine dimer residue Before After Figure by MIT OCW.Figure by MIT OCW