Ultrastructure of somatic and meiotic nucleoids.

In this review emphasis is placed on the contribution of transmission electron microscopy to the analysis of spread chromosomes and nucleoids. Support is advanced for the DNA loop and rosette organization of meiotic and metaphase chromosomes and nucleoids. Extensive discussion is given to the biochemical treatments used for producing nucleoids and the effect of divalent cations and chelating agents on chromatin compactization (supercoiling). Detailed studies on nucleoids from hepatocytes are presented, with emphasis on the significance of DNA attachment to the internal nuclear matrix and to the nuclear lamina. It is firmly predicted that from the increasing knowledge of the structural organization of eukaryotic chromatin and the genome, a greater understanding of the functional roles of the various intranuclear structures will ultimately follow.