In Vitro: MG 149 (Tip60 HAT inhibitor), at 200 μM, inhibited about 90% of Tip60 activity but had no inhibitory impact on p300 and PCAF. MG 149 was essentially competitive with Ac-CoA and noncompetitive with the histone substrate. HAT inhibition studies with MG 149 demonstrated that both compounds inhibited the HAT activity of the nuclear extracts of different regions significantly (p < 0.05).