Table 1. Mass spectrometric analysis of the total acetylation levels on H3K9 and H3K14 in retroviral Vec‐ or Cre‐infected PCAF−/−;GCN5flox/Δ MEFs
PeptideMH+ΔM (p.p.m.)Peak area ( × 106)Ratio (Vec/Cre)
VecCre
9KSTGG14KacAPR943.5320−1.40534.4638.60.84
9Kme1STGG14KacAPR957.5476−2.06541.0548.00.99
9Kme2STGG14KacAPR971.5633−0.911658.71956.80.83
9KacSTGG14KacAPR985.5425−2.22131.56.819.26
Sum of 14Kac2865.53150.20.91
  • The histone H3 proteins isolated from MEFs were digested with endoproteinase Arg‐C to release the 9KSTGG14KAPR peptide encompassing residues K9–R17 of histone H3. The peak area value represents the abundance of each type of modified peptides determined by mass spectrometry, with the relative standard deviation of ∼15%. Note that the peptide with acetylation on K9 alone, 9KacSTGG14KAPR, was undetectable. In other words, K9ac was always detected with co‐existing K14ac on the same peptide to form 9KacSTGG14KacAPR (H3K9/14ac). Therefore, the total level of H3K9 acetylation (H3K9ac) is represented by the H3K9/14ac level. At the shown high mass measurement accuracy (ΔM (p.p.m.)), tri‐methylated and acetylated lysine residues can be distinguished confidently by the mass spectrometer.