[The histone deacetylase activity of SIR2 and chromatin silencing]

Chromatin silencing is the inactivation of large domains of DNA by packaging them into a specialized inaccessible chromatin structure. This type of inactivation is involved in the regulation of gene expression and is also associated with the chromosome structures required for chromosome maintenance and inheritance. Silent information protein 2(SIR2) is one of the important proteins involved in chromatin silencing. It is clear that SIR2 has two coupled enzymatic activities, histone deacetylation and NAD breakdown activities, and produces a novel compound, O-acetyl-ADP-ribose in the enzymatic reactions. The histone deacetylation activity of SIR2 provides the direct link between SIR2 and the hypoacetylation of silent chromatin. Moreover, the relationship between the NAD cleavage and the deacetylase activity of SIR2 shows that the histone deacetylase activity is not its only crucial function. The breakdown of NAD C-N bond and the synthesis of O-acetyl-ADP-ribose may also be involved in chromatin silencing.