Chromatin higher order structure: opening up chromatin for transcription.

DNA packaged into chromatin is the physiologically relevant substrate for all DNA-dependent processes inside the nuclei of eukaryotic cells. The highly compacted structures of DNA and histones is inherently repressive for all DNA-dependent processes. Active mechanisms exist to generate dynamic chromatin, which maintains two apparently contradictory functions: tight compaction and free accessibility of DNA. The dynamics of chromatin higher order folding and the influence of chromatin structure on transcription will be described in this paper. Chromatin dynamics and higher order folding may be the key regulators of not only transcription but of all DNA-dependent processes in the nucleus.