Figure 3. Model for effect of divergent and convergent transcription.
A. As RNAP2 complexes converge, positive supercoiling builds up that is relieved by the type II topoisomerase activity of Top2. B. As RNAP2 complexes move away from each other in a divergent orientation, negative supercoiling is generated between them resulting in localized DNA melting and ssDNA formation, increasing the risk for damage to the DNA by endogenous or exogenous sources.