Human SIRT1-FL (A) and SIRT1-NT (B) purified from HEK293T cells enhance the activities of TDG. Lane 1, T/G-containing DNA substrate. Lane 2, 0.18 nM T/G-containing DNA substrate was incubated with 0.5 nM untreated hTDG Lanes 3–5 are similar to lane 2 but with added 0.5, 1, and 2 nM hSIRT1-FL (or hSIRT1-NT), respectively. Lane 6, T/G-containing DNA substrate was incubated with 2 nM hSIRT1-FL (or hSIRT1-NT) without TDG. The products were then treated with 0.1 M NaOH at 90°C for 30 min and separated on a 14% DNA sequencing gel. The images are pasted together from the same gel. Arrows mark the intact DNA substrate (I) and the cleavage product (N). Percentage (%) of product generated is shown below each lane. (C) Quantitative analyses of the fold of stimulation of hSIRT1-FL (open circles) and hSIRT1-NT (filled triangles) on the TDG glycosylase activity on T/G-containing DNA substrate from three experiments. The error bars reported are the standard deviations of the averages.