How does chromatin condensation keep the nucleus compact?
Packaging of approximately a meter-long DNA duplex within the elastic nucleus determines its spatial 3D architecture and the genomic accessibility of tissue-specific transcriptional programs. Apart from several biochemical processes, there are various forces at play in the chromatin organization, that in turn affect nuclear functions (reviewed in [1]). DNA micromanipulation experiments reveal that it has a persistent length of ~50nm and hence in an entropic configuration will have a radius of gyration ~300um due to electrostatic repelling as a consequence of its negative charge [2][3]. However, compaction of this flexible polymer inside a much smaller nucleus (~10-50um) is possible only because of the positively charged histones and other non-histone proteins that enable condensation, by stabilizing the electrostatic interactions [4][5].
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