O-acetyl-ADP-ribose (AAR) is a metabolic small molecule relevant in epigenetics that is generated by NAD-dependent histone deacetylases, such as Sir2. The formation of silent heterochromatin in yeast requires histone deacetylation by Sir2, structural rearrangement of SIR complexes, spreading of SIR complexes along the chromatin, and additional maturation processing. AAR affects the interactions of the SIR-nucleosome in vitro and enhances the chromatin epigenetic silencing effect in vivo. In this study, using isothermal titration calorimetry (ITC) and dot blotting methods, we showed the direct interaction of AAR with Sir3. Furthermore, through chromatin immunoprecipitation (ChIP)-on-chip and chromatin affinity purification (ChAP)-on chip assays, we discovered that AAR is capable of increasing the extended spreading of Sir3 along telomeres, but not Sir2. In addition, the findings of a quantitative real-time polymerase chain reaction (qRT-PCR) and examinations of an in vitro assembly system of SIR-nucleosome heterochromatin filament were consistent with these results. This study provides evidence indicating another important effect of AAR in vivo. AAR may play a specific modulating role in the formation of silent SIR-nucleosome heterochromatin in yeast.
