HTT and Huntington disease: Our data in Fig. 4b shows that the catalytic activity of kalirin toward Rac1 was significantly enhanced in the presence of Htt precipitates from WT mouse brain cytosol (7Q) and reduced in the presence of Htt precipitated from HD140Q/140Q mouse brain cytosol (140Q), suggesting that the function of kalirin for activating Rac1 could be compromised in HD brain.