Degradation of ribonucleic acid in mouse fibroblasts treated with actinomycin

High constitutive transcription of HSP86 gene in murine embryonal carcinoma cells

In order to investigate HSP86 heat-shock gene expression in embryonal carcinoma cell lines (EC), a partial mouse HSP86 cDNA clone was isolated and characterized. As observed for the corresponding protein, HSP86 RNA is shown to be constitutively more abundant in PCC4 and undifferentiated F9 EC cells than in fibroblasts, while its amount decreases upon F9 differentiation. Although mRNA stabilization is suggested to account in part of the high constitutive expression of the heat-shock-like protein HSC73 in F9 cells, HSP86 RNA appears as stable in fibroblasts as in F9 cells. Using run-on experiments we have established that high HSP86 expression in undifferentiated F9 cells in mainly due to enhanced transcription of the gene. Possible mechanisms responsible for this high level of transcription are discussed.

Actinomycin D and the hormonal induction of amylase synthesis in barley aleurone layers

The induction of amylase synthesis in barley aleurone layers by gibberellic acid is most sensitive to Actinomycin D (AM) over a short interval late in the lag phase. The duration of the lag phase may be extended as much as 3 fold by lower temperatures over the range 30° to 15° C. At each temperature the AM sensitive period remains close to the end of the lag phase, the period we have previously determined as the stage less sensitive to temperature.Lack of sensitivity to the inhibitor at other periods is not due to failure to penetrate, or to degradation. AM has no effect on tissue respiration, leucine, uridine or uracil uptake, leucine incorporation, or leucine pool size. At all stages it inhibits uracil and uridine incorporation into RNA. Thus AM probably acts by inhibiting RNA synthesis.

Kinetics of RNA synthesis in toad bladder epithelium: action of aldosterone during the latent period

Processing of RNA in the toad bladder was analyzed by polyacrylamide-gel electrophoresis to determine whether aldosterone causes any changes in the 1 hr before it potentiates transport of sodium ion. No change was found in the quantity or in the specific activity of bulk RNA labeled with uridine-5-(3)H. In vivo and in vitro with either uridine-5-(3)H or with methionine-(methyl)-(3)H as precursors, processing of RNA was extremely slow. Heterodisperse RNA was obvious after 30 min of continuous labeling, but labeling of the 40S precursor of ribosomal RNA was not apparent for 60 min. Labeling of mature 28S and 18S RNA first became apparent after 8 hr. approximately 7S RNA was the principal fastmigrating species labeled at 30 min, and 4S RNA was not heavily labeled until 1 hr. Aldosterone (5 x 10(-7) mole/liter) produced no changes. If care were not taken to inhibit metabolism of native bacteria colonizing the bladder, bacterial RNA of high specific activity predominated. We conclude that RNA metabolism in the toad bladder is extraordinarily slow, that a major acceleration of de novo synthesis in response to physiologic doses of aldosterone was not demonstrable, and that some reports to the contrary may have been influenced by artifacts from bacterial RNA metabolism. Earlier evidence for obligatory alterations in RNA metabolism during the latent period is not strong.

Stimulation of incorporation of nucleic acid precursors into HeLa cells caused by proflavine

1. The effect of proflavine and other acridines on the incorporation of precursors into the nucleic acids of HeLa cells was examined. 2. Relatively low concentrations (50mum) of proflavine completely inhibited incorporation of precursors into DNA, but allowed a small extent of incorporation into RNA. 3. Acridine-resistant incorporation into RNA was unaffected by actinomycin D at 2mug./ml. and persisted even at high concentrations (500mum) of many acridines. 4. A few combinations of acridine and precursor, notably 250mum-proflavine and [(14)C]adenine, caused a stimulation of incorporation. 5. The proflavine-stimulated incorporation was into alkali-stable di- and tri-nucleotides. 6. It was concluded that the effect was due to the preferential inhibition of degradation of a fraction of RNA that normally turned over, thus allowing small radioactive oligonucleotides to accumulate in the cells.

The loss of rapidly labelled ribonucleic acid from isolated HeLa cell nuclei

1. The loss of nucleic acids and protein from isolated HeLa-cell nuclei was studied. During 4hr. incubation at 37 degrees DNA was conserved, but appreciable amounts of RNA and protein were lost. 2. Two classes of nuclear RNA were distinguished: at least 75% of the RNA was lost from the nuclei relatively slowly through degradation to acid-soluble fragments; the rest of the RNA was lost much more rapidly, not only through degradation to acid-soluble fragments but also through diffusion of RNA out of the nuclei into the incubation medium. 3. The RNA that was preferentially lost was the fraction of nuclear RNA that was rapidly labelled when intact HeLa cells were grown in a medium containing radioactive precursors of RNA. 4. The RNA appearing in the incubation medium was apparently partially degraded and had a sedimentation coefficient of about that of transfer RNA. 5. Both the degradation of RNA and the loss of RNA from the nuclei were sensitive to bivalent cations. Low concentrations of Mg(2+) and Mn(2+) greatly increased the rate of degradation of the rapidly labelled RNA to acid-soluble fragments, and produced a corresponding decrease in the amount of RNA diffusing into the medium. At higher concentrations they suppressed both degradation and diffusion of RNA. The cations Ca(2+), Cu(2+), Zn(2+) and Ni(2+) all progressively inhibited both forms of loss of RNA. 6. Salts of univalent cations produced appreciable effects only at ionic strengths of about 0.2, when degradation to acid-soluble fragments was preferentially inhibited. 7. Both ADP and ATP inhibited loss of RNA at about 30mm. 8. It was concluded that the diffusion of rapidly labelled RNA out of the isolated nuclei was not related to the movement of RNA from nucleus to cytoplasm in vivo, but reflected the ease with which the rapidly labelled RNA detached from the chromatin and the permeability of the membranes of isolated nuclei.

The effect of ribonuclease on polysomes and ribosomes of bacteria and animal cells

The mildest treatment with ribonuclease that causes any disaggregation of the polysomes of Escherichia coli or HeLa cells simultaneously attacks the RNA of the constituent ribosomes. It is concluded that the susceptibility to ribonuclease of polysomes does not suggest that they are held together by a strand of messenger RNA. The RNA of the larger sub-unit of bacterial ribosomes has particularly sensitive regions resulting in a non-random degradation. The RNA of the smaller sub-unit of E. coli ribosomes is relatively resistant to ribonuclease attack. The same may be true of the respective sub-units of the intact HeLa-cell ribosome, but both sub-units become very sensitive to ribonuclease on dissociation from each other.

Effect of temperature of aldehyde fixation on the radioautographic localization of ribonucleoprotein in nucleoli of HeLa cells. Inhibition by puromycin and actinomycin D

In efforts to clarify the role of the nucleolus and substructures thereof in the assembly or synthesis of protein associated with formation of the complete ribosome, the effect of variation of some conditions of aldehyde fixation on the intranuclear distribution of lysine-(3)H, arginine-(3)H, and uridine-(3)H was studied by differential grain count in radioautographs of PPLO-free HeLa cells. It was found that the nucleolus is a site of rapid assembly or synthesis of a protein, the synthesis of which is inhibited equally by puromycin (200 microg/ml) and by actinomycin D under conditions inhibitory for ribosomal precursor RNA synthesis (P < 0.01). This protein is fixed by phosphate-buffered formalin or glutaraldehyde at pH 7.3, but the label is diminished by fixation in customarily employed acetic ethanol or in formalin at acid pH. Elevation of temperature of formalin or glutaraldehyde fixatives to 37 degrees C consistently reduces the nucleolar protein label, but not the RNA label, by a proportion identical with that incurred by puromycin or actinomycin inhibition. This proportional reduction of nucleolar protein label occurs without evident loss of total grain count and is independent of length of fixation between 30 min and 4 hr, but it is not observed at 23 degrees C. The data support the interpretation that the proportion of nucleolar protein not fixed at 37 degrees C is associated with nucleolar ribosomal RNA but that it is dissociated at 37 degrees C in formalin or glutaraldehyde fixatives, probably on the basis of ionic dissociation of a conjugated ribonucleoprotein.

Cytology of cultured cells surviving actinomycin D

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The effect of proflavine on HeLa cells

1. The effect of proflavine on the metabolism of RNA, DNA and protein of HeLa cells was studied. 2. The synthesis of RNA, DNA and protein was progressively inhibited by concentrations of proflavine up to 43mum. 3. There was no simple relationship between the degrees of inhibition of synthesis of RNA, DNA and protein by increasing concentrations of proflavine: the synthesis of RNA was most readily inhibited, and the synthesis of protein was relatively insensitive. 4. A concentration of 22mum-proflavine inhibited synthesis of RNA and DNA and caused a progressive loss of RNA from both nucleus and cytoplasm without any accompanying loss of DNA or dry weight from the cells. 5. The rapidly labelled RNA in the nucleus was preferentially degraded and was not transferred in a stable form to the cytoplasm.

Induction of tyrosine alpha-ketoglutarate transaminase by steroid hormones in a newly established tissue culture cell line

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Serum-induced formation of lysosomes in HeLa cells: a process sensitive to actinomycin D

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