Histone acetylation and the deoxyribonuclease I sensitivity of the Tetrahymena ribosomal gene.

Under appropriate conditions, up to 8.5% of the total acetate can be removed from the histones of isolated Tetrahymena macronuclei by an endogenous histone deacetylase activity. After in vitro deacetylation, the ribosomal genes are still preferentially digested by DNase I. These observations suggested that either the majority of histone-bound acetate is unnecessary to maintain the DNase I sensitive state or ribosomal chromatin (rChromatin) histones remain acetylated under these conditions. The characteristics of histones acetylation were studied in Tetrahymena rChromatin, which can be isolated in a relatively pure form. Histones associated with the presumably active, DNase I sensitive ribosomal genes have a high steady-state level of histone acetylation which, surprisingly, is maintained by very low acetate turnover rates.