NAD-dependent histone deacetylase, which contributes together with HST3 to histone H3 'Lys-56' deacetylation, regulation of telomeric silencing, proper cell cycle progression, DNA damage control, DNA recombination, and genomic maintenance. H2O + N(6)-acetyl-L-lysyl-[protein] + NAD(+) = 2''-O-acetyl-ADP-D-ribose + L-lysyl-[protein] + nicotinamide Binds 1 zinc ion per subunit. Present with 377 molecules/cell in log phase SD medium. Belongs to the sirtuin family. Class I subfamily.