Uptake of Polynucleotides by Mammalian Cells XV. Properties and Function of a DNA-Protein Complex Situated in the Outer Membrane of Ehrlich Ascites Tumor Cells

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Abstract
DNA-protein complexes are supposed to be original constituents of the membrane of [mouse] Ehrlich ascites tumor cells. These complexes can be attacked at the surface of viable cells by DNAse or protease. The DNA is partially embedded in protein structures. The net charge of this complex is of major importance for the RNA uptake capacity of the cells. Negatively charged DNA which is situated at the surface hinders RNA uptake. This is the explanation for the stimulation of RNA uptake by DNAse or the decrease in RNA uptake after protease treatment. Upon treatment of DNA-deficient complexes with homologous or heterologous DNA the original RNA uptake capacity of the cells is restored but the original conformation of the complex cannot be regained. The DNase action on the complex is temperature dependent in a sigmoidal fashion. It is markedly slowed down at temperatures below 12.degree. C. This implies that structural changes in the complex occur at this transition temperature which make surface DNA susceptible to DNAse. This effect can only be observed in original structures but not in reconstituted ones. Polyanion treatment of the cells [poly(L-lysine)] which increases their RNA uptake capacity, most probably does not interact with the DNA-protein complex. Poly(L-lysine) appears to act at other membrane sites. The DNA-protein complex was investigated entirely in situ, i.e., situated in the membrane of viable cells.

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