1. DNA topology: Topoisomerases keep it simple
Andrew D Bates, Anthony Maxwell 
Current Biology 
Volume 7, Issue 12, Pages R778-R781 (December 1997)
DOI: /S (06)

2. Figure 1
The reactions carried out by type II topoisomerases: (a) supercoiling/relaxation; (b) catenation/decatenation; (c) knotting/unknotting. All these transformations can be performed by the passage of one double-stranded DNA segment through another (double-headed arrows).
Current Biology 1997 7, R778-R781DOI: ( /S (06) )

3. Figure 2
A schematic illustration of the reaction of topoisomerase IV with DNA catenanes. The steady-state mixture of catenated and unlinked products formed in the presence of topo IV and ATP contains a lower proportion of catenanes than the equilibrium mixture formed by the cyclisation of P4 DNA in the presence of pAB4 plasmid. Catenanes are in red, and unlinked DNA circles are in green.
Current Biology 1997 7, R778-R781DOI: ( /S (06) )

4. Figure 3
The model proposed by Rybenkov et al. [1] for the ATP-driven decatenation reaction of type II topoisomerases. The enzyme (blue) binds to the G segment and another distant site, at which ATP hydrolysis can drive the enzyme along the DNA, constraining the T segment in a smaller loop and making its capture more probable. The notch in the enzyme indicates the ATP-operated clamp and the arrows indicate the ATP-dependent movement of DNA.
Current Biology 1997 7, R778-R781DOI: ( /S (06) )