The Sirtuins (Sir2-like proteins), originally described as the "silencing information regulator 2" in S . cerevisiae", are a family of highly conserved proteins that function as NAD⁺-dependent histone deacetylases. They are involved in gene silencing, DNA replication, DNA repair, cell survival, and aging. These eukaryotic proteins can be divided into four classes, designated I-IV; Class I is composed of SIRT1-3, Class II, SIRT4; Class III, SIRT5; and Class IV, SIRT6-7. SIRT1 has been shown to have the highest homology to Sir2. Given the interrelationship between the levels of NAD⁺ the cell's energy state and aging, there is much interest in SIRT1. Specifically, SIRT1 has been shown to bind to and regulate a number of transcription factors and is known to deacetylate 53, a tumor suppressor protein. SIRT1 deacetylates p53, but it does not play a role in cell survival following DNA damage. While the exact role that SIRT1 plays in the regulation of p53 and cell survival remains to be elucidated, the use of SIRT inhibitors may serve as useful tool in this area of research.