This invention relates to methods of screening compounds that modulate cellular and organismal processes by modification of the activity of SIR2 and/or transcription factors, e.g., p53, particularly methods of screening for compounds that modify lifespan and/or metabolism of a cell or an organism by modulation of the activity of SIR2 and/or transcription factors, e.g., p53, and more particularly to methods of screening for compounds that modulate the activity of Sir2 and/or transcription factors, e.g., p53. In particular, the present invention relates to a method for screening a compound, by providing a test mixture comprising a transcription factor, Sir2, and a Sir2 cofactor with the compound, and evaluating an activity of a component of the test mixture in the presence of the compound. The invention further relates to therapeutic uses of said compounds. The invention further relates to a method of modifying the acetylation status of a transcription factor binding site on histone or DNA by raising local concentrations of Sir2.