John H. Frenster
The Rockefeller Institute, New York, New York

Interphase chromatin fractions, either repressed or active in RNA synthesis, were isolated from calf thymus lymphocytes (Frenster, Allfrey, and Mirsky, Proc. Natl. Acad. Sci. 1963, 50: 1026). The ratios of total histones, hydrophobic non-histone proteins, total RNA, and total phospholipids to the DNA within each chromatin fraction were determined, and were expressed as the quotient of these ratios in active chromatin divided by the corresponding ratios in repressed chromatin of the same animal. The average active/repressed quotient for total histones was 0.9, for hydrophobic non-histone proteins 2.0, for total RNA 5.1, and for total phospholipids 4.8, indicating a nearly equal partition of total histones between the DNA of active and that of repressed chromatin. Lysine-rich histones constituted 20 per cent of total histones within each chromatin fraction. Total histone electrophoresis patterns on cellulose polyacetate and total phospholipid chromatography patterns on silicic acid were similar for the two types of chromatin.

Isolated repressed and active chromatin fractions were incubated with ATP-8-C¹⁴ or UTP-8-C¹⁴ to measure RNA synthesis after isolation. It was observed that the isolated chromatin fractions retained their repressed or active character throughout isolation and subsequent incubation. Addition of RNA, phospholipids, and/or hydrophobic non-histone proteins to such incubations had a stimulatory effect on repressed chromatin, but little or no effect on active chromatin.

These data are compatible with the concept that interphase DNA is largely repressed in complex formation with histones, and that the DNA active in RNA synthesis is de-repressed by molecular species which antagonize the DNA-histone interaction.

Supported by an award (CA-17857) from the USPHS.

1. Frenster JH, "Structural Continuity between Active and Repressed Chromatin within Interphase Lymphocytes", J. Cell Biol. vol. 23, no. 3, p. 117a, (1964).

2. Frenster JH, "Ultrastructural Continuity between Active and Repressed Chromatin" Nature 205: 1341 (1965).

3. Frenster JH, "Nuclear Polyanions as De-repressors of Synthesis of Ribonucleic Acid", Nature 206: 680 (1965).

4. Frenster JH, "Mechanisms of Repression and De-Repression within Interphase Chromatin", In Vitro, vol. 1, pp. 78-101 (1965).