The biosynthesis of the five main histone fractions of rat thymus

[Study On The Chromosomal Proteins Of Fasciola Hepatica]

In attempt to investigate histone fractions and non-histones of parasites, nuclei were isolated from Fasciola hepatica by the procedure of Pogo et al. (1966). Histone fractions H1, H2a, H2b, H3 and H4 were prepared from isolated nuclei by the procedure of Johns (1964 and l967). The five histone fractions found in most tissues were also present in the Fasciola hepatica histones. These histone fractions were characterized by amino acid analysis and by polyacrylamide disc gel electrophoresis. Non-histone proteins were extracted from isolated Fasciola hepatica nuclei and separated by SDS-polyacrylamide gel electrophoresis. The results of the experiment were summarized as follows: 1. The yield of whole histone recovered was 2.47 mg per 1 g of Fasciola hepatica. 2. The yield of DNA was 1.02 mg per gm of tissues. Consequently the DNA to histone ratio was 1:2.44. 3. The relative amounts of five fractions, i.e., Hl, H2a, H2b, H3 and H4 were 19.96%, 26.48%, 29.60%, 12.56% and 14.37%, respectively. 4. Amino acid analysis of the individual histone fractions showed that the over-all compositions were similar but not identical to those of corresponding fraction from calf thymus. 5. It was found that histone H2b fraction of Fasciola hepatica contained detectable amounts of epsilon-N-monomethyllysine. No evidence for the presence of methylated lysine or other side-chain derivatives was reported on this histone fraction. 6. In SDS-polyacrylamide disc gel, it showed that 17 protein bands of nuclear acidic protein can be identified visually.

Metabolic activities of histones in rat liver and spleen

Synthesis and turnover of histone I and II in normal rat liver and spleen were studied by Amberlite CG 50 column chromatography. Histone I was separated into three or four subfractions, each of which showed a different rate of incorporation of [3H]lysine. This was verified by a more shallow gradient chromatography developed by Kinkade and Cole [3] for very lysine-rich histone (F1), which showed tissue specific differences between liver and spleen in both the elution pattern and synthetic rates. These subfractions were distinguished from each other by dodecylsulphate electrophoresis. The turnover, or disassociation of histone I and II in chromatin was measured by double-labelling of normal rat liver with [3H] and [14C]lysine. A good correspondence was found between the synthesis and turnover patterns of individual histone I fractions, while the histone II synthesized was conserved for over a month. From consideration of the turnover in relation to the cell population of normal liver tissue, which consists of a very small fraction of growing cells and a very large fraction of resting ones, it was concluded that turnover of histone I must occur even in resting cells. When DNA synthesis in the spleen was completely inhibited by hydroxyurea, the synthesis of histone II was inhibited but that of histone I was only partially inhibited. The remaining synthesis seemed to occur in cells in the resting state. It was concluded tentatively, the continuous replacement of very lysine-rich histones of chromatin must occur even in resting cells in which DNA synthesis has ceased. The biological significance of disassociation of histones from chromatin was discussed.

The synthesis and decay of histone fractions and of deoxyribonucleic acid in the developing avian brain

1. The turnover of cerebral histones and DNA after injection of [4,5-(3)H]leucine or [methyl-3-(3)H]thymidine, respectively, was studied in the developing chick. 2. Chromatin was prepared from chick nuclei that had been purified by centrifugation through 1.9m-sucrose. 3. Nuclear proteins were fractionated into three major histone classes, F1 (lysine-rich), F2(b) (slightly lysine-rich) and [F3+F2(a)] (arginine-rich), and a non-histone protein residue. 4. The proportions of the histone classes remained constant throughout the period of development studied. 5. All histone fractions decayed at a similar rate, initially with a half-life of around 5 days, later with a half-life of 19 days. 6. Non-histone proteins from chromatin decayed in a heterogeneous manner with a wide range of half-lives. 7. Short-term labelling studies showed that all histone fractions were synthesized at the same rate. 8. Some non-histone proteins were very rapidly synthesized relative to histones. 9. DNA had a longer half-life than any histone fraction studied. A biphasic exponential decay curve with half-lives of 23 and 50 days was found. 10. It was concluded that the turnover of histones can occur independently of that of DNA and that different histone classes have similar rates of synthesis and decay.

Transient stimulation of deoxyribonucleic acid-dependent ribonucleic acid polymerase and histone acetylation in human embryonic kidney cultures infected with adenovirus 2 or 12: apparent induction of host ribonucleic acid synthesis

The synthesis of cell-specific ribonucleic acid (RNA) appeared to be stimulated in human embryonic kidney (HEK) cultures infected with adenovirus 2 or 12. Deoxyribonucleic acid (DNA)-RNA hybridization experiments revealed that by 44 to 70 hr after infection with either virus, the relative amount of pulse-labeled RNA capable of hybridizing with HEK cell DNA increased considerably; such RNA was detected in both nuclear and cytoplasmic fractions. The main increase in apparent host RNA synthesis was preceded by (i) a relatively early transient stimulation of the DNA-dependent RNA polymerase activity in isolated nuclei, and (ii) a small but consistently observed increase in the rate of acetylation of lysine-rich and arginine-rich histone fractions. The Mn(2+)-(NH(4))(2)SO(4) and Mg(2+)-activated RNA polymerase reactions measured in nuclei isolated from cells infected with adenovirus 2 or 12 were stimulated at about the same time; a rapid loss of polymerase activity followed. The augmentation of the two RNA polymerase reactions found in adenovirus 12-infected cells was independent of protein synthesis. After the initial increase, the acetylation rate of histones of cells infected with adenovirus 2 or 12 declined, until late in infection it was approximately 40 to 70% of the control cell rate.