SET domain-containing protein 7/9 (SET7/9) is a histone methyltransferase that monomethylates lysine 4 of histone H3, which generates a specific tag for epigenetic transcriptional activation. It plays a role in the transcriptional activation of tumor suppressor p53 in response to DNA damage, as well as the transcription factor TAF10. (R)-PFI-2 is a potent, cell-permeable inhibitor of SET7/9 (IC50 = 2 nM) that demonstrates greater than 1,000-fold selectivity over a panel of 18 other methyltransferases. (S)-PFI-2, the inactive enantiomer, is 500-fold less potent (IC50 = 1 μM) and may serve as a negative control. See the Structural Genomics Consortium (SGC) website for more information.