FIG 7.
Topoisomerase activity of wild-type and truncated IntSSV2 proteins. Wild-type or truncated IntSSV2 was incubated for 4 h at 65°C with negatively supercoiled pBR322 DNA (0.6 μg). The samples were treated with proteinase K and SDS and subjected to electrophoresis in a 1.2% agarose gel. The gel was stained with ethidium bromide and photographed under UV light. Lanes 1 to 8 show enzyme concentrations of 0.125, 0.25, 0.5, 1, 2, 4, 8, and 16 μM, respectively. N80 + C81 and N164 + C165 indicate N80 and N164 mixed with C81 and C165, respectively, at a molar ratio of 1. Topo I indicates a positive control in which pBR322 DNA was relaxed with calf thymus topoisomerase I (10 U). For lane C, IntSSV2 was omitted. Positions of negatively supercoiled (S.C.) and relaxed (Rel) plasmids are indicated.