Structure and properties of rat-thymus deoxyribonucleoprotein. A comparison of the electric birefringence and other properties of deoxyribonucleoprotein prepared by various methods

1. A comparison has been made of the properties of dNP (deoxyribonucleoprotein) prepared in various ways from rat thymus. The variables studied were: (a) extent of homogenization; (b) concentration of various metal ions; (c) concentration of EDTA; (d) extent of dialysis; (e) concentration of dNP. The chief method used for studying the dNP was that of electric birefringence; this gives information about the optical and electrical properties of molecules oriented in an electric field and about their length. 2. The extent of homogenization during the preparation affects the birefringence properties only slightly and the solubility properties of the constituent DNA not at all. However, the protein content of the dNP decreases after repeated homogenization. 3. In the presence of added Ca(2+), Mg(2+) or Na(+) an insoluble product is obtained. 4. The presence of added EDTA affects the birefringence properties only slightly. 5. In the final stage of preparation, both very limited dialysis and extensive dialysis (in terms of volume ratio) cause partial insolubility of the final product. 6. dNP prepared at low concentrations resembles in some respects dNP prepared at higher concentrations and then subjected to limited enzyme action but it is not degraded (as by extensive enzyme action); ultracentrifuge studies of the constituent DNA confirm that no degradation of the DNA has occurred. 7. It is concluded that dNP prepared at low concentrations or by extensive dialysis is denatured and that preparation of ;native' material is favoured by maintenance of a high dNP concentration and by fairly limited dialysis.     

Ultracentrifuge studies of histone fractions from calf thymus deoxyribonucleoprotein

Molecular weights and sedimentation coefficients of four major fractions of calf thymus histones were measured. The minimum molecular weights were determined in concentrated solutions of guanidine hydrochloride. The results indicate that, with the possible exception of fraction F3, the fractions are heterogeneous. Comparisons in 0.1m-sodium chloride suggest that fraction F1 does not aggregate and show that fractions F2(a) and F3 aggregate to form larger complexes than does fraction F2(b). The degree of aggregation of each fraction is independent of pH in the range pH1-7. Detailed studies with fraction F2(b) have confirmed that the change in sedimentation coefficient observed as the sodium chloride concentration of the solution is increased results from increases in the apparent molecular weight of the sedimenting units. It has been found that the molecules of fraction F2(b) are present as single molecules only in sodium chloride solutions of 33mm or less. At these low concentrations the effects of charge greatly increase the concentration dependence of the sedimentation rate; the results can, however, be interpreted by using the theory developed by Alexandrowicz & Daniel (1963) and Daniel & Alexandrowicz (1963).     

Dose-dependent effects of carbendazim on rat thymus

In this study, the effects of carbendazim on the thymus in male rats were evaluated. Carbendazim was administered at 0, 150, 300 and 600 mg kg(-1) day(-1) doses by gavage to male rats for 15 weeks. Body weights of rats in all groups were recorded weekly during treatment. At the end of the experiment, the effects of carbendazim on the thymus were investigated histopathologically and morphologically. Also, based on these effects, change in immunolocalization of fibronectin (FN), which is a component of the extracellular matrix, was investigated immunohistochemically. Fibrosis and oedema were observed in the thymus of rats treated with 300 and 600 mg kg(-1) day(-1) doses of carbendazim. Also in this region, an increase in FN density was noted at the end of the immunohistochemical investigation. A decrease was observed in absolute and relative thymus weights of rats treated with carbendazim compared with the control group. While the decrease in absolute thymus weight was statistically significant in rats exposed to carbendazim at the highest dose, the decrease in relative thymus weights was statistically significant for all carbendazim doses.     

Effects of irradiation on RNA synthesis primed by calf thymus deoxyribonucleoprotein treated with salt and salt-urea.

1. The effects of ionizing radiation on the activity of calf thymus templates were examined in a Escherichia coli RNA polymerase system. 2. The template activity of native and 2 M NaCl-5M urea-treated deoxyribonucleoproteins was enhanced by relatively low doses of irradiation, while that of 2 M NaCl-treated deoxyribonucleoprotein was not enhanced by irradiation. 3. The template activity of purified DNA was markedly decreased by irradiation, while that of native deoxyribonucleoprotein, 2 M NaCl-treated, and 2 M NaCl-5 M urea-treated ones were slightly decreased at a higher dose range. The doses for 50% inactivation of these templates were 1.3, 210, 140, and approximately 200 krad, respectively.     

Structure and repair of rat thymus DNA during long-term irradiation

During long-term fractionated irradiation (0.5 Gy, daily) the molecular weight of single-stranded DNA of the thymus of exposed rats remained the same as that of intact animals till the dose of 25 Gy had been cumulated. The integrity of the DNA structure was ensured by the repair of DNA and elimination of cells with unrepaired lesions. The role of repair decreased and the elimination of cells increased with increasing cumulative dose.     

Metabolic properties of histones from rat liver and thymus gland

1. The incorporation of ¹⁴C-labelled amino acids into acid-extractable proteins from rat-liver and -thymus nuclei confirmed the existence of a protein component with a higher uptake than that into the major histone components. 2. This rapidly labelled component appeared to contain the thiol groups detectable in the acid extracts. 3. Histone f1 contained 1mol. of serine phosphate/mol. of mol.wt. of 42000–43000. 4. Phosphate was present in other components of the 50mm-hydrochloric acid extract from liver and thymus nuclei, and was probably associated with the thiol-containing component. 5. The difference in amino acid uptake into the histones of diffuse and dense chromatin was confirmed. Dense chromatin was found to have a higher proportion of disulphide than did diffuse chromatin.