Substrate sequence requirements and regions on SIRT1 necessary for activation. (A and B) SIRT1 activation by STAC-2 on peptides derived from PGC-1α–K778 (A) and FOXO3a-K290 (B) as measured by PNC1-OPT assay; data are means ± SEM (n = 3). (C) Biochemical screen for activation-compromised mutants. A bacterial expression plasmid (pET28a) carrying the SIRT1 gene was mutagenized and used to generate recombinant SIRT1 proteins that were screened for activity in the presence or absence of resveratrol using an AMC-based assay. (D) Activation of wild-type SIRT1, E230K, and E230A mutants by 40 μM resveratrol, 50 μM STAC-1, 5 μM STAC-2, 5 μM STAC-3, and 10 μM STAC-4 as measured by an AMC assay; data are means ± SD (n = 3). Dimethyl sulfoxide (DMSO) was used as a control.