Size analysis of heterogeneous nuclear RNA in an aqueous gel system

Structure of transcriptionally active chromatin: radiological evidence for requirement of torsionally constrained DNA

Synthesis of alpha- and beta-globin RNA in DMSO-induced Friend's erythroleukemia cells and synthesis of immunoglobulin gamma- and kappa-chain RNA, total RNA, 5S RNA, and tRNA in mouse myeloma cells (MPC-11) was inhibited by gamma-irradiation. For all RNA species, synthesis decreased nearly exponentially as a function of radiation dose, whereas RNA size distributions, turnover rates, and specific activities of radioactively labeled RNA were affected only insignificantly. D37 values for the loss of synthesis of various RNA species correspond to target sizes ranging from 21,000 to 53,000 kd, or 30-80 kbp of DNA. These target sizes are several-fold larger than the structural genes in question; however, they correspond well with the size of DNA loops, or "domains" constrained by the nuclear matrix. The data suggest that the eukaryotic transcription unit is the torsionally constrained chromatin loop, transcription of which may be inactivated, or significantly reduced by a DNA single-strand break.

In vivo studies on the age-dependent decrease of the rates of total and mRNA synthesis in the brain cortex of rats

The membrane hypothesis of aging (Zs.-Nagy, I., 1978, J. Theor. Biol. 75, 189-195) attributes the primary role in cellular aging to an age-dependent decrease of the passive potassium permeability of the cell membrane which is due most probably to free-radical damage of the membrane components. As a consequence, the intracellular and intranuclear ionic strength increases resulting in a condensation of the chromatin and a slowing down of the synthetic processes performed by the nucleus. In this concept it was of importance to reveal whether the rates of total and mRNA synthesis display any age-dependent alteration parallel with the change of membrane permeability of the brain nerve cells. Experiments were performed using tritiated uridine incorporation measurements and suitable preparation techniques in young, adult and old rats (1.5, 13 and 25 mth of age, respectively). Comparisons of the incorporation rates revealed a very considerable decrease in the rate of synthesis of both the total and polyadenylated RNA (polyA + RNA) between the ages of 13 and 26 mth. The old animals displayed only about 55 and 67% of the rate of synthesis for the 2 classes of RNA, respectively, as compared to the young and adult rats, if the results are expressed as dpm/mg RNA. However, the decreases are even more pronounced (34 and 41%) if the results are expressed on a dry weight basis. The results obtained are compatible with the membrane hypothesis of aging.