The effect of proflavine on HeLa cells

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.

Regulation of the initiation of hemoglobin synthesis in the blood island cells of chick embryos. V. Qualitative studies of the effects of proflavine

Most blastodiscs explanted before the 1-somite stage of development onto medium containing 20 μg of proflavine/ml failed to form any detectable hemoglobin, whereas the majority explanted at later stages formed hemoglobin visible to the naked eye. Formation of hemoglobin by 2-somite blastodiscs was suppressed by proflavine at 50 μg/ml, but 6-somite blastodiscs formed visible quantities of hemoglobin. Incorporation of leucine into protein was inhibited by proflavine, and almost the same amount of inhibition was produced at both concentrations of inhibitor for all developmental stages examined.Net incorporation of uridine into acid-precipitable material was moderately inhibited by 20 μg of proflavine/ml, and almost totally suppressed by 50 μg of proflavine/ml. Only polynucleotides of low molecular weight accumulated in blastodiscs treated with either concentration of proflavine, but preformed stable RNA's were not degraded in the presence of inhibitor. Proflavine appeared to inhibit synthesis of, or cause degradation of, new RNA of high molecular weight at both concentrations. Accumulation of RNA of low molecular weight continued at a low proflavine concentration, but little additional RNA accumulated at a high proflavine concentration.