Maximum likelihood phylogeny of the class I sirtuin family. Numbers indicate bootstrap support based on 100 replicates. SIRT1: Sirtuin 1; SIRT2: Sirtuin 2; SIRT3: Sirtuin 3. Colored boxes indicate annotated and/or predicted subcellular locations of the proteins: nucleus (purple), cytoplasm (yellow) and mitochondria (green). SIRT3 in Rattus norvegicus and Mus musculus lost the mitochondrial N-terminal targeting signal and thus were retained in the cytoplasm.