Fig. 6.

TDP2 substrates all include a 5′-phenolic ring. (A) Physiological substrates include 5′-tyrosyl covalent bonds with Top2α and Top2β (left) [121] and the replicative picornavirus protein VPg [124] (2nd from left). Top3α and β are plausible candidates as well. (B) Top1 covalent complexes are processed much less efficiently [121,133]. (C): Substrate used for biochemical experiments and drug screening: T5PNP [153], NPPP [154] and digoxygenin [134].