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. 2014 Apr 28;53(19):3229–3236. doi: 10.1021/bi500421q

Figure 8.

Figure 8

Etoposide quinone is a covalent poison of topoisomerase IIβ. In the left panel, etoposide quinone enhancement of DNA cleavage is not reversed by the addition of reducing agents after DNA cleavage complexes have been established. DNA cleavage reactions were carried out in the absence (blue bars) or presence (open blue bars) of DTT. Reaction mixtures contained no drug (ND) or 30 μM etoposide quinone in mixtures that included DTT at the time of DNA cleavage (Pre EQ) or DTT that was added (for an additional 6 min) after cleavage complexes were formed (Post EQ). In the right panel, etoposide quinone does not form DNA lesions that poison topoisomerase IIβ. DNA was incubated without (−EQ, open orange bars) or with (+EQ, orange bars) 30 μM etoposide quinone. DNA was purified from free drug and used in DNA cleavage reactions mediated by topoisomerase IIβ. DNA cleavage reactions were performed in the absence of drug (ND) or in the presence of 30 μM etoposide quinone (EQ). In all cases, error bars represent the standard deviation of three independent experiments.