Fig. 1.

Role of SIRT1 and SIRT6 in chromatin condensation. SIRT1 and SIRT6 promote formation of heterochromatin in three ways. Firstly, both of the sirtuins deacetylate H3K9 enabling its trimethylation and subsequent binding of HP1α indispensable for heterochromatin formation. Secondly, SIRT1 decreases activity of p300 histone acetyltransferase. Lastly, SIRT1 activates Suv39h1 methyltransferase by deacetylating K266 in its catalytic domain. Moreover, SIRT1 inhibits polyubiquitination of Suv39h1 by MDM2 and prevents its degradation. Arrows indicate positive regulation. Lines with T-shaped ending indicate inhibition. Thick upward and downward arrows inside boxes indicate increase or decrease during aging, respectively. (Color figure online)