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

The use of antibiotics in the culture of non-sterile plant protoplasts

The use of antibiotics to control infections in cultures of protoplasts of leaf mesophyll cells has been examined. The antifungal agents nystatin and amphotericin B were non-toxic to protoplasts at concentrations that controlled fungal growth (25 units and 2.5 μg/ml respectively). Of the antibacterial agents examined, only carbenicillin and, to a lesser extent, gentamicin were active against the bacteria usually encountered whilst still permitting normal protoplast metabolism and regeneration. The most satisfactory control of contaminating microorganisms was obtained with a combination of nystatin (25 units/ml) or amphotericin B (2.5 μg/ml) and carbenicillin (250 μg/ml).

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.