Transcription by eukaryotic RNA polymerases A and B of chromatin assembled in vitro.

Chromatin was assembled in vitro from simian virus 40 DNA form I and the calf-thymus four histones H2A, H2B, H3 and H4. Transcription with calf thymus RNA polymerases A and B (I and II) was greatly inhibited. Nucleosomes were found to inhibit both RNA chain initiation and elongation. The inhibition of elongation could be relieved by increasing ionic strength, suggesting that electrostatic interactions between histone octamer and DNA have to be broken for RNA polymerase to transcribe DNA organised into nucleosomes.