A homologous family of proteins that includes the NAD-dependent protein deacetylases which deacetylate proteins by catalyzing the formation of O-acetyl-ADP-ribose from the ADP-RIBOSE moiety (of NAD) and the acetyl group that is being removed from the protein. Sir2p, from Saccharomyces cerevisiae, is the founding member and the family includes other homologs (HSTs - homologs of Sir Two). Some HISTONE DEACETYLASES (the Sir2-like HDACs) belong to this family of proteins.