Figure 3.

HOS3 is much less sensitive to the deacetylase inhibitor TSA than the related deacetylases HDA1 or RPD3. Activities containing HOS3, HDA1, and RPD3 were obtained by immunoprecipitation from yeast nuclear extracts as described previously (1). HOS3 from E. coli was obtained from the peak fraction in Fig. 2A (fraction 28). [³H]acetyl-Hela histones (50,000 cpm) were incubated with each of the deacetylases for 30 min and assayed as described previously (1). Inhibition of deacetylase activity at various concentrations of inhibitor was calculated as a ratio of enzyme reactions containing TSA vs. no TSA. Maximal conversion of the [³H]acetyl-Hela histones to the release of free acetate was maintained below 2% to reduce the effect of substrate limitation on the apparent inhibition by TSA.