Dissecting the Nucleosomal Barrier to Transcription

The nucleosome, which represents the fundamental unit of chromatin and an intrinsic regulator of transcription, consists of a histone octamer and ∼150 base pairs of DNA. The histone proteins in turn contain two functional regions: the histone-fold domains, which make strong contacts with the DNA and organize it into the superhelical structure specific to the nucleosome, and the histone tails, which are highly positively charged and can stabilize the nucleosome further. Both histone regions, but especially the tails, are the target of many posttranslational modifications associated with gene expression. © 2011 Biophysical Society. Published by Elsevier Inc