Some observations on the structure, cation content and possible evolutionary status of dinoflagellate chromosomes
1984
Sigee, David C.
SICEE, D. C., 1984. Some observations on the structure, cation content and possible evolutionary status of dinoflagellate chromosomes. Dinoflagellate chromosomes have a well‐ordered structure, as observed in living cells, glutaraldehyde/osmium tetroxide‐fixed cells, ultrathin cryosections and freeze‐etch preparations. It is suggested that the stabilization of this chromatin in the living cell is largely mediated by divalent cations, acting as bridging molecules between the DNA superstructure and the protein matrix. Studies using X‐ray micro‐analysis and autoradiography have shown that these chromosomes have high levels of bound Ca and transition metals, and that these are associated with both the DNA and surrounding proteins. The organization and stabilization of chromatin in dinoflagellate chromosomes is quite different from that of the cells of other eukaryotes, but shows some resemblance to the dispersed chromatin of bacteria. The evolution of dinoflagellate chromosomes from a prokaryote‐like ancestral genome is attributed to two main factors–the retention of a primitive cationic non‐histone stabilization system, and a pronounced evolutionary trend towards high DNA values. On this theory, dinoflagellate chromosomes are phylogenetically distinct from all other eukaryote chromosomes, and provide a separate evolutionary route for the attainment of high DNA levels and increased cell size.
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