Identification of top1 as Et743-inducible DPC protein. (A) Purification strategy (see details in Materials and Methods). (B) SDS/PAGE DPC assay of fraction 22–24 after Mono S column chromatography. Lanes 1, 3, and 5 are without Et743; lanes 2, 4, and 6 are with 0.1 μM Et743. (C) Typical 8% SDS-polyacrylamide gel and silver staining of aliquots from fractions 22–24 (lanes 7–9, respectively) after Mono S chromatography. (D) top1 immunoblotting of the post-Mono S fractions 22–24. Lane 10 corresponds to a truncated form (86 kDa) of purified top1. (E) Covalent complexes formed by purified recombinant top1 in the presence of Et743. Autoradiography of a typical SDS/PAGE: lane 14, DNA alone; lane 15, + top1; lanes 16, + top1 + 0.1 μM Et743; lane 17, + top1 + 10 μM CPT.