Presented at the Tenth Annual Meeting of the American Society for Cell Biology, San Diego, California, November 19-21, 1970, and Published in : J. Cell Biol. vol. 47, p.65a (1970):

"Correlation Between the Ultrastuctural Binding Site of Nuclear Ligands and the Effect of the Ligand on RNA Synthesis in Human Leukocytes".

John H. Frenster
Department of Medicine, Stanford University School of Medicine, Palo Alto, California

E-mail:   frenster@euchromatin.net


Abstract:

Certain nuclear ligand molecules (phytohemagglutinin [PHA], HgCl2) increase RNA synthesis within human leukocytes, whereas other nuclear ligands (acridine orange [AO], actinomycin) inhibit RNA synthesis in these cells. Normal and leukemic human bone marrow cells were reacted with 10 -3M AO before or after fixation. Normal human lymphocytes were incubated with tritiated PHA (10 mm/ml) or with 10 -5 M HgCl2. Bound AO or HgCl2 was visualized by electron microscope reaction products (1969. J. Cell Biol. 43: 39a). Bound PHA-3H was visualized by electron microscope radioautography (1968. J. Cell Biol. 39: 129a; 1970. Clin. Res. 18: 189). AO was found to be confined to DNA receptor sites within the active extended euchromatin of the cell nucleus, whereas PHA-3H and HgCl2 were found localized chiefly in the condensed repressed heterochromatin of the cell nucleus, apparently on histone receptor sites (references above; 1966. Biochem. J. 98: 888). These data indicate that DNA within active euchromatin is more reactive to AO than is DNA within repressed heterochromatin. Conversely, histones within active euchromatin appear less reactive to PHA-3H or HgCl2 than do histones within repressed heterochromatin. The current model of selective gene de-repression within mammalian cells (1965. Nature 206: 1269) predicts such variable reactivity of DNA and of histones when euchromatin is compared with heterochromatin, on the basis of native conformational states in the living cell which expose DNA within active euchromatin while shielding histones, and which expose histones within repressed heterochromatin while shielding DNA (ibid). The known effects of the nuclear ligands on RNA synthesis and on the hetrochromatin-euchromatin transition are a consequence of such preferential binding within exposed binding sites in the living cell nucleus.
[Supported by NIH grant CA-10174].

1. Ord MG, and Stocken LA, "Metabolic Properties of Histones from Rat Liver and Thymus Gland", Biochem. J., vol. 98: 888-897 (1966).

2. Yamane T, and Davidson N, "On the Complexing of Desoxyribonucleic Acid (DNA) by Mercuric Ion", J. Am. Chem. Soc., vol. 83, 2599-2607 (1961).

3. Pauly JL, Caron GA, and Suskind RR, "Blast Transformation of Lymphocytes from Guinea Pigs, Rats, and Rabbits induced by Mercuric Chloride in vitro", J. Cell Biol. vol. 40, 847-850 (1969).


Additional References:

1. Frenster JH, "Electron Microscope Localization of Acridine Orange Binding within Nuclei of Human Leukemic Bone Marrow Cells", J. Cell Biol. vol. 43, p. 39a (1969).

2. Frenster JH, "Electron Microscopic Localization of Acridine Orange Binding to DNA within Human Leukemic Bone marrow Cells", Cancer Res. vol. 32, pp. 1128-1133 (August, 1971).

3. Frenster JH, "Selective Control of DNA Helix Openings during Gene Regulation", Cancer Res. vol. 36: pp. 3394-3309 (September, 1976).

4. Frenster JH, "Activation of DNA Transcription within Repressed Chromatin", 14th John Innes Symposium, September 5-8, 2001.


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euchromatin:  "the most active portion of the genome within the cell nucleus".