AP sites can stimulate the
formation of covalent Topo IV–DNA complexes. The DNA cleavage
assay using Topo IV (24 nM) and the T440 DNA containing an AP site
as DNA substrate (0.8 nM) was performed and the DNA products were
analyzed as described in Materials and Methods. AP sites were located within
the 4 base overhang generated by DNA scission (A)
and immediately outside the two points of scission (B).
Experiments were repeated three times and representative results
are shown. The results of the quantification are shown in Table
1. Lane 0, T440(0); lane –2, T440(–2); lane –1,
T440(–1); lane 1, T440(+1); lane 2, T440(+2);
lane 3, T440(+3); lane 4, T440(+4); lane 5, T440(+5);
lane 6, T440(+6). Size markers were 5′-end-labeled
64 and 31 nt oligos.