Nucleosome unwrapping and unstacking.

Access to the eukaryotic genome is key to the regulation of such DNA processes as transcription, replication and repair. About three-quarters of the human genome is stored and shielded within arrays of nucleosomes, the fundamental structural units of chromatin, each of which contains about 150bp of DNA and an octameric histone protein composed of two each of H2A, H2B, H3 and H4. Structural fluctuation of nucleosomes provides regulatory proteins with transient access to the internal DNA; however, nucleosome unwrapping, sliding and unstacking must occur to obtain full access of the DNA. In this review, we focus on the unwrapping of mononucleosomes and internucleosomal interactions to discuss our current understanding of the dynamics of the process.