Fig. 6. Proposed model for XPC-GFP behavior in living cells. In nonirradiated cells, XPC constantly shuttles between nucleus and cytoplasm. In the nucleus, it interacts very transiently with DNA. In UV-irradiated cells, the shuttling is stopped, increasing the concentration in the nucleus. In addition, XPC continues probing DNA. Once damage is encountered, the binding time increases considerably, probably because of stabilization of the DNA-protein complex by binding of subsequent NER factors such as TFIIH and XPA.