Liou Gunn-Guang, Tanny Jason C, Kruger Ryan G, Walz Thomas, Moazed Danesh
Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115.
Department of Biochemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115.
Cell. 2005 May 20;121(4):515-527. doi: 10.1016/j.cell.2005.03.035.
Assembly of silent chromatin domains in budding yeast involves the deacetylation of histone tails by Sir2 and the association of the Sir3 and Sir4 proteins with hypoacetylated histone tails. Sir2 couples deacetylation to NAD hydrolysis and the synthesis of a metabolite, O-acetyl-ADP-ribose (AAR), but the functional significance of NAD hydrolysis or AAR, if any, is unknown. Here we examine the association of the Sir2, Sir3, and Sir4 proteins with each other and histone tails. Our analysis reveals that deacetylation of histone H4-lysine 16 (K16), which is critical for silencing in vivo, is also critical for the binding of Sir3 and Sir4 to histone H4 peptides in vitro. Moreover, AAR itself promotes the association of multiple copies of Sir3 with Sir2/Sir4 and induces a dramatic structural rearrangement in the SIR complex. These results suggest that Sir2 activity modulates the assembly of the SIR complex through both histone deacetylation and AAR synthesis.
芽殖酵母中沉默染色质结构域的组装涉及Sir2对组蛋白尾部的去乙酰化作用以及Sir3和Sir4蛋白与低乙酰化组蛋白尾部的结合。Sir2将去乙酰化作用与NAD水解及代谢产物O-乙酰-ADP-核糖（AAR）的合成偶联起来，但NAD水解或AAR（若有）的功能意义尚不清楚。在此，我们研究了Sir2、Sir3和Sir4蛋白彼此之间以及与组蛋白尾部的结合情况。我们的分析表明，组蛋白H4赖氨酸16（K16）的去乙酰化作用在体内对沉默至关重要，在体外对Sir3和Sir4与组蛋白H4肽段的结合也至关重要。此外，AAR本身促进多个Sir3拷贝与Sir2/Sir4的结合，并在SIR复合物中诱导显著的结构重排。这些结果表明，Sir2活性通过组蛋白去乙酰化作用和AAR合成来调节SIR复合物的组装。
