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PubMed1984

Inhibition of the biosynthesis of deoxyribonucleic acid, ribonucleic acid and protein in HeLa S3 cells by cucurbitacins, glucocorticoid-like cytotoxic triterpenes.

Cucurbitacins were found to inhibit the incorporation of radioactive precursors into DNA, RNA and protein in intact and permeabilized HeLa S3 cells. The observed inhibition was rapid and irreversible although the maximal effect (almost complete inhibition) required several hours of cell exposition to the agent. The magnitude of the inhibition was, with some exceptions, nearly the same for all three precursors within the entire range of cucurbitacin concentrations examined. The ID50 values (concentrations required to produce half-maximal inhibition of the macromolecule biosynthesis) determined for several cucurbitacins were very close to their respective ED50 values (those for half-maximal inhibition of cell proliferation). Parallel with the inhibition of [3H]-labelled precursor incorporations into nucleic acids, cucurbitacin diminished the [3H]thymidine and [3H]uridine nucleotides' pool sizes of HeLa S3 cells. No effect of cucurbitacin on the [3H]leucine pool was observed. The studies presented prove that cucurbitacins inhibit the biosynthesis of DNA, RNA and protein in HeLa S3 cells, and that these inhibitory effects are closely related to the inhibition of HeLa S3 cell proliferation by cucurbitacins. The mechanism of the inhibition is unknown but the obtained results suggest that cucurbitacins act upon an unidentified target, which results in the inhibition of macromolecule biosynthesis. It was also found that these inhibitory effects of cucurbitacins are neither mediated by glucocorticoid receptors nor require replication, transcription or translation.

Antineoplastic Agents↗
PubMed1982

Kinetics for exchange of imino protons in deoxyribonucleic acid, ribonucleic acid, and hybrid oligonucleotide helices.

The lifetime for opening of individual base pairs in a DNA (dCA5G + dCT5G), and RNA (rCA5G + rCU5G), and a hybrid DNA-RNA (rCA5G + dCT5G) helix have been measured by proton nuclear magnetic resonance. The lifetimes were obtained by saturation recovery experiments performed on the hydrogen-bonding imino protons of the Watson-Crick base pairs. In these oligonucleotide helices the observed relaxation rates were dominated by exchange with water, with the magnetic spin-lattice relaxation time of the imino protons possibly being important only at the lowest temperatures in the DNA helix. It was shown that three interior base pairs in the DNA heptamer dCA5G + dCT5G were in the open-limited region, which means that these imino protons exchange every time the base pair opens. The lifetime of the terminal G X C base pairs in the DNA helix are much shorter than the interior A X T base pairs. The pH dependence of the terminal base pairs indicated that the ends of the helix open and close many times before exchange of the imino protons with water takes place. The temperature dependence of the lifetimes of the interior A X T imino protons in the DNA helix showed that these protons exchange only when the double helix has dissociated into single strands. Thus, these lifetimes measure the rate for dissociation of the double helix. The activation energy for this process was found to be 47 kcal/mol. Comparison of the lifetimes of the interior protons in the DNA, RNA, and hybrid helices showed that the rates of dissociation of the RNA and hybrid helices are very similar at 5 degrees C, whereas the rate for the DNA helix was approximately 1 order of magnitude smaller than that for the other two helices. The reasons for the differences in the kinetics of the three helices are discussed, as are the general dynamics of oligonucleotide helices in solution.

Base Sequence↗
PubMed1966

Changes in dry weight, protein, deoxyribonucleic acid, ribonucleic acid and reserve and structural carbohydrate during the aerobic growth cycle of yeast.

1. Changes in dry weight, DNA, RNA, protein and reserve and structural carbohydrate were measured during the aerobic growth of yeast on 0.9% glucose in an aerobic synthetic medium. 2. After glucose had been consumed and during the growth of yeast on ethanol and acetate, the rate of formation of DNA remained about the same but the rate of increase of dry weight was greatly diminished. 3. During the second stage of growth the ratios dry weight/DNA, protein/DNA, RNA/DNA and carbohydrate/DNA decreased to about 30% of the corresponding values during the first stage of growth. 4. A higher fraction of the dry weight of the yeast cells could be accounted for by the reserve carbohydrate content of the cells during the second stage of growth. 5. By the end of the first stage of growth an increase in the reserve carbohydrate content of the cells was observed. Part of this reserve carbohydrate was consumed by the cells in the beginning of the second stage of growth. The possibility of adaptation of cells at the expense of their reserves is discussed.

Carbohydrate Metabolism↗
PubMed1968

The binding of o-aminoazotoluene to deoxyribonucleic acid, ribonucleic acid and protein in the C57 mouse.

1. (3)H-labelled o-aminoazotoluene was synthesized from [G-(3)H]o-toluidine on a semi-micro scale. 2. An association of (3)H with DNA, RNA and protein from the liver, kidney and spleen of female C57b mice was demonstrated after the administration of a single dose of [(3)H]o-aminoazotoluene. 3. This association is judged to represent covalent binding as a result of experiments involving solvent extraction, examination of the acid hydrolysates of the DNA and RNA and administration of [(3)H]water with unlabelled o-aminoazotoluene. 4. Examination of the extents of binding at various times after the administration of a single dose of [(3)H]o-aminoazotoluene showed that there was a peak of binding to liver DNA in the female mice at about 16hr. that was not present in the male mice. 5. The extent of binding to DNA, RNA and protein at 16hr. in the female C57b mouse liver was greater than that in the spleen and kidney.

Animals↗
PubMed1970

Examination of an equilibrium interpretation of deoxyribonucleic acid-ribonucleic acid hybridization data.

1. When a constant amount of denatured DNA is annealed for a constant time with a series of different RNA concentrations, it is often observed that the reciprocal of the amount of RNA hybridized is linearly proportional to the reciprocal of the RNA concentration. This may be explained by assuming that an equilibrium is set up between free RNA and DNA on the one hand and DNA-RNA hybrid on the other. The hybridization of Escherichia coli DNA and ribosomal RNA was used to test this proposition. Rate constants were estimated from the initial rates of the forward and back reactions and compared with direct estimates of the dissociation constant. 2. The rate constants of the forward and back reactions were estimated to be 1.82mlmug(-1)h(-1) (160lmol(-1)s(-1)) and 0.023h(-1) (6.4x10(-6)s(-1)) respectively, giving a ratio k(2)/k(1)=0.013mugml(-1). After 24h annealing the dissociation constant was estimated to be 0.114mugml(-1), and by extrapolation to infinite time, 0.047mugml(-1). 3. It is concluded that (a) equilibrium greatly favours the hybrid complex, (b) equilibrium is not established in 24h, (c) the equilibria that were directly estimated are incompatible either with the measured rates of the forward and back reactions or with the simple formulation of the reaction that was adopted, and finally (d) for these reasons the equilibrium interpretation of the linear reciprocal relationship is unsatisfactory.

Citrates↗
PubMed1976

The theory of the deoxyribonucleic acid - ribonucleic acid hybridization reaction.

A general equation is derived describing data of DNA-RNA hybridization in the presence of a competing self-annealing reaction of RNA. The well known double-reciprocal relation and the Scatchard equation are shown to be limiting cases of this general equation. Some new hybridization data at various temperatures are presented and analysed by using the new equation. The results can only be explained if we assume that the behavior of DNA towards single RNA molecules is the same as that towards the annealed form, (RNA12. The variation of the equilibrium constant of the hybridization reaction with temperature is small, indicating a small heat of reaction. The maximum amount of hybridized RNA at equilibrium appears to be independent of temperature.

DNA↗
PubMed1992

Correlated responses in lines of chickens divergently selected for fifty-six-day body weight. 2. Organ growth, deoxyribonucleic acid, ribonucleic acid, and protein content.

Growth of organs relative to body weight and cellular protein, RNA, DNA, and cell unit size of breast muscle, liver, and small intestinal tissue were measured in females from four lines of chickens. Two lines had undergone 32 generations of divergent selection for 56-day body weight, and the other two lines were derived by sampling the first two lines at Generation 28 and relaxing selection for the next five generations. The diet used in the present experiment was the same diet under which selection was practiced (20% crude protein and 2,685 kcal of ME/kg). Comparisons at common chronological ages and a common body weight revealed that supply organ weights, especially that of the small intestine, were associated with subsequent growth of demand organs. Although the upper gastrointestinal tract was also important in this respect, it was more susceptible to influences such as feed intake. Selection for juvenile body weight resulted in correlated changes in cell size of breast muscle but not liver and small intestine. Muscle increased posthatch as cells underwent hypertrophy but liver and small intestine grew chiefly by hyperplasia.

Animals↗