Purity >95%. Gcn5 is a chromatin modifying factor whose HAT activity is required to acetylate histone H3 lysine 9 (K9) and K14, which facilitates transcription elongation by relaxing nucleosomes. Butyrolactone 3 specifically inhibits the histone acetyltransferase Gcn5 with an IC50 value of 100 μM and has an affinity to the Gcn5 enzyme comparable to that of its natural substrate, histone H3. Butyrolactone 3 can inhibit pre-RNA splicing with an IC50 value of 0.5 mM and as such has been used to investigate Gcn5/PCAF-like HAT functions during assembly of spliceosome before pre-mRNA translation.