"In-Vivo DNase I-Sensitive Sites Within Intact Human Bone Marrow Cells."

John H. Frenster,
Physicians' Educational Series, Atherton,CA 94027-5446

DNA molecules undergo localized helix openings during active gene transcription (Ann. N.Y. Acad. Sci. vol. 567, p. 334 (August 4, 1989), and these openings can be detected within single intact cells by DNase-I digestion and high-resolution probe electron microscopy (Cancer Res. vol.31, p. 1128 (August, 1971). Human bone marrow cells were aspirated and rapidly fixed within 5 sec. in cold glutaraldehyde, followed by acridine orange probe insertion and DNase-I digestion. DNase I-sensitive sites ranged in length from 25-700 nm., corresponding to 70-2000 base pairs in length of DNA. These sites were found to be confined to the extended euchromatin microfibrils of the cell nucleus, where they correlate most closely in location with sites of active gene transcription. Marrow cells in early maturation and interphase were found to have large numbers and large sizes of DNase I-sensitive sites, while marrow cells in late maturation or in cell division were found to have reduced numbers and sizes of sites. These sites of highly localized openings in the DNA helix offer targets for molecular interaction with de-repressor RNA species of ribo-regulators during gene transcription (1-7). It is concluded that DNase I-sensitive sites are confined to the active euchromatin portion of the cell nucleus, where their number and size parallel the rates of m-RNA synthesis and gene transcription at these sites.
Additional References:

1. Frenster JH, Allfrey VG, Mirsky AE, Repressed and Active Chromatin Isolated from Interphase Lymphocytes. Proc Natl Acad Sci (USA) 50, 1026-1032 (1963).

2. Frenster JH, Ultrastructural Continuity Between Active and Repressed Chromatin. Nature 205, 1341-1342 (1965).

3. Frenster JH, Nuclear Polyanions as De-Repressors of Synthesis of RNA.
Nature 206, 680-683 (1965).

4. Frenster JH, A Model of Specific De-Repression within Interphase
Chromatin. Nature 206, 1269 (1965).

5. Frenster JH, Localized Strand Separations within DNA during Selective
Transcription. Nature 208, 894-896 (1965).

6. Frenster JH, Correlation of the Binding to DNA Loops or to DNA Helices with the Effect on RNA Synthesis. Nature 208, 1093-1094 (1965).

7. Lemanski LF, Nakatsugawa M, Bhatia R, Erginel-Unaltuna N, Dube DK,
A Specific Synthetic RNA Promotes Cardiac Myofibrillogenesis in the Mexican Axolotl. Abstract #3640. Molecular Biology of the Cell, 7, 626a
(December, 1996).

8. Hendzel MJ, Kruhlak MJ, and Bazett-Jones DP, Organization of Highly Acetylated Chromatin around Sites of Heterogenous Nuclear RNA Accumulation. Molecular Biology of the Cell, 9, 2491-2507 (September, 1998).

9. Stewart RD, Model for the distribution of DNA Among Chromatin States (Heterochromatin, transcriptionally inactive Euchromatin, transcriptionally active Euchromatin, and nascent (just-replicated) Euchromatin).

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