Introduction 1 3 1 2 4 1 3 5 6 1 1 2 5 7 9 10 11 2 1 5 2 7 12 14 1 15 16 8 17 18 19 20 2 1 1 Experimental Methods and materials 4a 4b 5a–d 7 8 T m 2 3 Streptomyces 6 −1 2 4 2 4 −1 2 −1 2 UV spectroscopy −1 2 4 2 4 −1 2 2 λ CD spectroscopy −1 −1 2 4 2 4 −1 2 2 Kinetic measurements −1 2 4 2 4 −1 2 High-performance liquid chromatography −1 −1 2 −1 Electrospray mass spectrometry −1 2 4 2 4 −1 2 2 −1 m z m z Results and discussion 2 4a 4b 5a–d Fig. 1 1 2 3  2 4a 2 T m 4a T m 2 2 2 4a 3 T m 3 4a 2 T m 1 Fig. 2 4a 2 −1  4b T m 4b 2 T m T m 3 2 2 1 Fig. 3 4b 2 −1  4a 2 4 4a 4a 2 4a 2 Fig. 4 4a grey black 2 −1 dashed line  2 4a 2 5 4a 2 4a 2 4a 2 1 3 2 5 Fig. 5 4a 2 a b 4a  2 4b 4a 4b 2 1 6 1 2 4a 4b 2 7 8 21 22 Fig. 6 4b 2 a b  Table 1 Examined oligomers and adduct formation DNA oligomers   Adduct formula adduct 6− a adduct 6− a b AATTACGTAATT 4a 161 202 43 90 11 752.32 / 752.33 755.99 / 755.99 53 CAATTATAATTG 4b 161 202 43 90 11 752.32 / 752.39 755.99 / 756.00 10 AATTAGTAATT 5a 152 190 40 84 10 704.15 / 704.16 707.81 / 707.83 13 AATTTGAAATT 5b 152 190 40 84 10 704.15 / 704.16 707.81 / 707.82 5 AATTTGTAATT 5c 152 191 37 86 10 702.65 / 702.65 706.31 / 706.31 16 AATTAGAAATT 5d 152 189 43 82 10 705.65 / 705.66 709.31 / 709.32 1 a b 4a 2 1 7 Fig. 7 4a 2 23  2 5a–d 2 5a–d 2 2 1 2 5a–d 6 7 T m 6 7 2 T m 2 2 6 7 7 8 6 2 8 Fig. 8 6 7 2 a b  2 24 30 2 5d 5d 2 9 3− 4− 5− 6− 9 m z 1 19 20 27 31 5 m z 6 m z 5d 5 2− 6 T 2− 2− 31 m z 10 4− 10 1 m z 10 4− 10 1 10 4− m z 10 4− m z 9 Fig. 9 a T 5d 2 b 5d c T 5d 2 d 5d  Scheme 1 Proposed cleavage reaction of DNA–trioxacarcin A adduct  19 5d 2 1 1 10 8 5 9 6 9 5d 4a–b 5a–c 4a 4b 5a–c 5a 5d Conclusions 2 2