ABSTRACT
Areas of the histone folds are presented at the outer face of the histone octamer and are thus able to make contact with DNA. All the interactions of the histone folds are with the inner face of the DNA supercoil and extend over 121 bp. However, there is still uncertainty about the absolute contribution made by interactions to the overall stability of the DNA-histone octamer complex because other structural elements within the histone amino acid sequences also seem to be involved in DNA binding. The addition of a linker histone into the compaction process not only constrains an additional 20 bp of DNA but also determines the trajectory of the DNA entering and leaving the nucleosome, which in turn directs the relative positioning of successive nucleosomes. The vast majority of genes are incorporated into euchromatic regions of chromosomes, so our discussion of how the cell can extract information from compacted chromatin will focus initially on this more accessible chromatin architecture.
