Structure of transcriptionally active chromatin

Rat-liver chromatin has been fractionated into transcriptionally active and inactive regions [Gottesfeld et al. (1974) Proc. Nat. Acad. Sci. USA 71, 2193-2197] and the distribution of nuclease-resistant complexes in these fractions has been investigated. About half of the DNA of both fractions is resistant to attack by the endonuclease DNase II. The nuclease-resistant structures of inactive chromatin are DNA-histone complexes (v-bodies) which sediment at 11-13 S. Template-active chromatin yields two peaks of nuclease-resistant nucleoprotein. These complexes sediment at 14 and 19 S, and contain DNA, RNA, histone, and nonhistone chromosomal proteins. Polyacrylamide gel electrophoresis reveals a complex pattern of chromatin proteins, suggesting that the complexes are heterogeneous in composition