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‘Epichromatin’, the surface of chromatin beneath the interphase nuclear envelope (NE) or at the surface of mitotic chromosomes, was discovered by immunostaining with a specific bivalent mouse monoclonal anti-nucleosome antibody (mAb PL2-6). ‘Chromomeres’, punctate chromatin particles approximately 200–300 nm in diameter, identified throughout the interphase chromatin and along mitotic chromosomes, were observed by immunostaining with the monovalent papain-derived Fab fragments of bivalent PL2-6. The specific target for PL2-6 appears to include the nucleosome acidic patch. Thus, within the epichromatin and chromomeric regions, this epitope is ‘exposed’. Considering that histones possess unstructured ‘tails’ (i.e. intrinsically disordered peptide regions, IDPR), our perception of these chromatin regions becomes more ‘fuzzy’ (less defined). We suggest that epichromatin cationic tails facilitate interactions with anionic components of NE membranes. We also suggest that the unstructured histone tails (especially, histone H1 tails), with their presumed promiscuous binding, establish multivalent binding that stabilizes each chromomere as a unit of chromatin higher order structure. We propose an ‘unstructured stability’ hypothesis, which postulates that the stability of epichromatin and chromomeres (as well as other nuclear chromatin structures) is a consequence of the collective contributions of numerous weak histone IDPR binding interactions arising from the multivalent nucleosome, analogous to antibody avidity.


Originally published:
Olins DE, Olins AL. 2018 Epichromatin and chromomeres: a ‘fuzzy’ perspective. Open Biol. 8: 180058.

© 2018 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution License, which permits unrestricted use, provided the original author and source are credited.

Supplementary file retrieved from:
Olins, Donald E.; Olins, Ada L. (2018): Supplementary material from "Epichromatin and chromomeres: a ‘fuzzy’ perspective". The Royal Society. Collection. (4570 kB)
Supplementary material (.mov file) from "Epichromatin and chromomeres: a ‘fuzzy’ perspective"



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