FIG. 8.

Transcription collision model for proteasomal degradation of Top I-DNA covalent complexes. In this model, the collision between the Top I-DNA covalent complex and the elongating RNA polymerase complex triggers proteasomal degradation of both Top I and RNA Pol II₀. Degradation of Top I-DNA covalent complexes results in exposure of single-strand breaks. Degradation of RNA Pol II₀ may signal repair (4, 26). Repair of the exposed single-strand breaks presumably occurs via TCR. ub, ubiquitin.