Reversible acetylation of the chromatin remodelling complex NoRC is required for non-coding RNA-dependent silencing

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Abstract
The chromatin remodeller NoRC silences rDNA by establishing heterochromatin. TIP5, a subunit of NoRC is acetylated by MOF and deacetylated by SIRT1 at Lys 633. Acetylation decreases TIP5 binding to rDNA promoter-associated RNA, leading to altered heterochromatin formation. TIP5 acetylation can be modified by changes in metabolism. The SNF2h (sucrose non-fermenting protein 2 homologue)-containing chromatin-remodelling complex NoRC silences a fraction of ribosomal RNA genes (rDNA) by establishing a heterochromatic structure at the rDNA promoter1,2,3. Here we show that the acetyltransferase MOF (males absent on the first) acetylates TIP5, the largest subunit of NoRC, at a single lysine residue, K633, adjacent to the TIP5 RNA-binding domain, and that the NAD+-dependent deacetylase SIRT1 (sirtuin-1) removes the acetyl group from K633. Acetylation regulates the interaction of NoRC with promoter-associated RNA (pRNA), which in turn affects heterochromatin formation, nucleosome positioning and rDNA silencing. Significantly, NoRC acetylation is responsive to the intracellular energy status and fluctuates during S phase. Activation of SIRT1 on glucose deprivation leads to deacetylation of K633, enhanced pRNA binding and an increase in heterochromatic histone marks. These results suggest a mechanism that links the epigenetic state of rDNA to cell metabolism and reveal another layer of epigenetic control that involves post-translational modification of a chromatin remodelling complex.