Figure 6. SIRT6 promotes resolution of DNA double strand breaks (DSBs).. (a-c) Impaired resolution of DSBs in SIRT6 knock-down (S6KD2) cells. Control (pSR) and knock-down (S6KD) cells were isolated 1 hour after NCS treatment and tail moment was determined in comet assays. (a) Histogram of tail moments of >100 cells. (b) Representative comet images from S6KD or control cells following DNA damage (+NCS) or mock (-NCS) treatment. (c) Mean tail moment of comet assays shown in (a). Error bars indicate the S.E.M. (d) Wild-type SIRT6 (S6WT), but not the mutant SIRT6 (S6HY), protein rescues the DSB repair defect of SIRT6 knock-down cells. Mean tail moment of comet assays for the indicated cells, following treatment with NCS and quantified as in (c). (e) Resolution of site-specific DNA DSBs in SIRT6 KD (S6KD2) and control (pSR) cells assayed using the I-SceI and I-PpoI systems. Quantitative real-time PCR amplification of DNA using primers flanking the DSB sites is shown. *, p=0.009; **, p=0.02. The data represent the average of triplicate experiments, and error bars indicate the S.E.M.