(f) Immunoblot analysis of liver cell extracts (applied in serial dilutions) obtained from mice fed with 3 mM spermidine for 200 days and respective control mice of the same age. Blots were probed with antibodies recognizing total histone H3 (C-terminal epitope) or specific for acetylated lysine 18 residue (N-terminal epitope). Full scans of blots are available in Supplementary Information, Fig. S5. 