Several factors that participate in DNA damage response and repair are SUMOylated (reviewed in Dou et al. 2011, Bekker-Jensen and Mailand 2011, Ulrich 2012, Psakhye and Jentsch 2012, Bologna and Ferrari 2013, Flotho and Melchior 2013, Jackson and Durocher 2013). SUMOylation can alter enzymatic activity and protein stability or it can serve to recruit additional factors. For example, SUMOylation of Thymine DNA glycosylase (TDG) causes TDG to lose affinity for its product, an abasic site opposite a G residue, and thus increases turnover of the enzyme. During repair of double-strand breaks SUMO1, SUMO2, SUMO3, and the SUMO E3 ligases PIAS1 and PIAS4 accumulate at double-strand breaks where BRCA1, HERC1, RNF168, MDC1, and TP53BP1 are SUMOylated. SUMOylation of BRCA1 may increase its ubiquitin ligase activity while SUMOylation of MDC1 and HERC2 appears to play a role in recruitment of proteins such as RNF4 and RNF8 to double strand breaks. Similarly SUMOylation of RPA1 (RPA70) recruits RAD51 in the homologous recombination pathway.