Benzene metabolites inhibit topo II–DNA binding.

Oligonucleotides, containing a strong topo II binding site from positions 87 to 126 of pBR322, were annealed and end-labeled with [α-³²P]dCTP. Nuclear extract (1 μg protein) from HeLa cells was assayed for binding activity to the ³²P-labeled binding site in the presence of 0.1 μg poly(dI:dC) • (dI:dC). The DNA-protein complex (bound) was separated from free probe (free) by electrophoresis through a nondenaturing, 4% polyacrylamide gel in 0.25 × Tris borate–EDTA buffer. Nuclear extract was incubated with increasing concentrations (1, 10, 30, 100, and 300 μM) ofp-benzoquinone (A), hydroquinone (B), and peroxidase-activated hydroquinone (C) prior to initiating the reaction with labeled oligonucleotide.