Studies on the mechanism of transcription of nucleosomal complexes.

The mechanism of transcription by Escherichia coli RNA polymerase holoenzyme of chromatin assembled in vitro has been studied by two approaches. Using digestion with endodeoxyribonuclease EcoRI as a probe of mobility, it was found that nucleosome movement is slow compared to the time taken for RNA polymerase to transcribe through regions organised into nucleosomes. However, transcription leads to at least some displacement of nucleosomes relative to their original site on the DNA. In the second approach chromatin was reconstituted from extensively crosslinked histone octamers and simian virus 40 DNA. RNA chain elongation on this template is inhibited relative to non-crosslinked chromatin. This can be related to a decrease in the ability of the cross-linked histone octamers to dissociate from the DNA.