Regulation of histone acetylation in Tetrahymena macro- and micronuclei.

Histone acetylation in Tetrahymena macro- and micronuclei has been studied utilizing a combination of electrophoretic and autoradiographic techniques. Histones H2A, H2B, H3, and H4 are acetylated to varying extents in the transcriptionally active macronucleus. There are few, if any, acetylated subspecies of these histones in the transcriptionally inert micronucleus, and micronuclei incorporate little radioactive acetate, either in vivo or in isolated nuclei. Butyrate is shown to inhibit histone deacetylation in Tetrahymena, both in vivo and in isolated nuclei. Incorporation of acetate into micronuclei is unaffected by high concentrations of this inhibitor, indicating that the extremely low levels of histone acetylation observed in micronuclei are not due to rapid deacylation but probably result from the absence of histone acetylation. We also present evidence that macronuclear core histones are composed of at least two classes of molecules distinguishable on the basis of their acetate turnover rates and that individual histone species differ in the distribution of their populations between these classes.