Fig. 2

Regulation of PCNA by ubiquitin and Sumo. When cells are treated with high doses of MMS, PCNA becomes Sumo-modified primarily on K164 and to a lesser extent K127, resulting in recruitment of HR inhibitor Srs2. At lower levels of DNA damage PCNA is ubiquitinated mainly on K164 (and to a lesser degree also on other sites [113, 51]). This promotes lesion bypass in case of monoubiquitination, whereas polyubiquitinated PCNA induces template switching and error-free DNA repair