NAD-dependent protein deacetylase which modulates the activities of several proteins which are inactive in their acetylated form. Deacetylates the N-terminal lysine residue of Alba, the major archaeal chromatin protein and that, in turn, increases Alba's DNA binding affinity, thereby repressing transcription. H2O + N(6)-acetyl-L-lysyl-[protein] + NAD(+) = 2''-O-acetyl-ADP-D-ribose + L-lysyl-[protein] + nicotinamide Binds 1 zinc ion per subunit. The two SIR2 homologs in this organism, Af1 and Af2, display different substrate specificities in vitro. Af2 can deacetylate histones and peptides corresponding to the C-terminal part of p53 in a NAD-dependent manner (PubMed:12408821). Belongs to the sirtuin family. Class III subfamily.