Aggregation insensitive eukaryotic chromatin in which DNA is associated with histones can be crosslinked by all fixatives commonly used in electron microscopy. By crosslinking it becomes protected from aggregation during dehydration with organic solvents. This is not the case with most nonorthodox chromatins, where the ratio of protein to DNA is estimated to be 5 to 10 times lower and where the basic, acid-soluble proteins are rather different from the histones. The aggregation sensitivity of different chromatins is summarized in table 1.Nonorthodox aggregation sensitive chromatins were found in Eubacteria, bacteriophage- pools (fig. 1a,b), Cyanobacteria, mitochondria, and Dinoflagellates (fig. 2a,b). The latter organisms are of particular interest because of morphologic similarities to other flagellates like Euglena with its aggregation insensitive histone-containing chromosomes (fig. 3a,b). With respect to the distribution over the living world, nonorthodox chromatins might be more frequent than the histone-containing ones.

Pelzer, J., Bohrmann, B., Johansen, R., Maeder, M., Gyalog, R., Arnold-Schulz-Gahmen, B., Villiger, W., & Kellenberger, E. (1990). Structure and function of nonorthodox chromatins: I. aggregation sensitivity of DNA is correlated to the Protein content of chromosomal material. Proceedings, Annual Meeting, Electron Microscopy Society of America, 48(3), 120–121.