<p>Supplemental Figures and Figure Legends.</p><p>Supplemental Figure 1. Specificity of H3K23 antibodies.</p><p>(A) Characterization of the anti-H3K23-propionylation antibody by dot blotting. The histone peptides as indicated at the left were immobilized on the membrane and probed with anti-H3K23-propionylation antibody. H3 (K23-Pr): a H3 peptide from </p><p>Lys18 to Arg26 with Lys23 propionylated; H3 (K23-Ac), Lys18 to Arg26 with Lys23 acetylated; H3 (un-modified): from Lys18 to Thr32 without any modification.</p><p>(B) Detection with anti-H3K23-acetylation antibody (Upstate, # 07-355). Peptides spotted on the membrane were the same as in A above. Supplemental Figure 2. Evaluation of H3K23 propionylation in different cell lines.</p><p>(A-C) Spectra of d3_Acetyl derivatized K18/K23-modified peptides from different cell lines.</p><p>(D) Information of four quantifying peptides from A-C above. The quantification equation is shown below the table. Supplemental Figure 3. Evaluation of H3K23 propionylation during monocytic differentiation.</p><p>Histones were purified from U937 cells without PMA induction and U937 and HL60 </p><p> cells with PMA induction. Shown are the LC/MS/MS spectra of d3_acetyl derivatized </p><p>K18/K23 peptides. The peak at m/z 544.47 (2+) corresponds to the K23-propionylated</p><p>18 23 peptide KAcDQLAT KPrAAR. Supplemental Figure 4. No enzyme control of the in vitro H3K23 depropionylation assay.</p><p>Shown is the MALDI-TOF spectrum of propionylated peptide that has been incubated in HDAC buffer for 60 min without Sirtuin 1. Note that no depropionylation peak was detected. Supplemental Figure 5. Sir proteins Sirtuin 2 and 3 can also depropionylate </p><p>H3K23 in vitro.</p><p>(A) Time courses of depropionylation and deacetylation of H3K23-modified peptides by Sirtuin 2 and Sirtuin 3. Experiments were performed three times. The STD is shown as the error bars. The deacetylation or depropionylation percentages were calculated by following equations:</p><p>K23 deacetylation = Intensitypeak1089.6 / Total intensitypeak1089.6 & peak1131.6; </p><p>K23 depropionylation = Intensitypea1089.6 / Total intensitypeak1089.6 & peak1145.5.</p><p>(B-C) MALDI-TOF spectra of acetylated (B) and propionylated peptides (C) incubated in HDAC buffer for 60 min without Sir2 proteins. Note that no deacetylation or depropionylation peak was detected.</p>