Fig. 2.

Topo IIIα and Blm can resolve the DHJS. There was no detectable activity on the substrate with either Topo IIIα alone (lane 2) or Blm alone (lane 3). When both proteins are added to the reaction, resolved DNA circles can be detected (lane 4). This activity depends on the activity of the Topo IIIα, because Topo IIIα with a mutated active-site tyrosine (mut) cannot support resolution (lane 5); it also depends on the helicase activity of Blm, because omission of ATP from the reaction buffer also abolishes activity (lane 6). Markers A and B are for the resolved products (lanes 7 and 8).