Fig. 1. Hypothesis for a step-wise mechanism to resolve arrested Pol II elongation complexes. Two examples of arrested Pol II complexes and how they might be resolved are shown. On the right is an elongation complex arrested at a DNA lesion, and on the left is a complex arrested for other reasons. General elongation factors such as TFIIS play an important role for the resolution of the latter complex but have little effect on damage-stalled Pol II. By contrast, CSB/Rad26 can affect the resolution of both types of complexes. If such resolution fails, ubiquitin- (and Def1-) related mechanism come into play. This does not necessarily always involve Pol II proteolysis, which might only be the final solution to the problem.