Étude au microscope électronique de l'interaction de l'acide désoxyribonucléique et des polyamines

Abstract

Interactions between polyamines and deoxyribonucleic acid are studied by means of electron microscopy on thin sections and by spreading method. With high concentrations of polyamines (5 × 10 −3 M or more) in aldehydic fixing fluids, DNA molecules become aggregated and consist mainly of coarse fibres which are generally highly interconnected. Low concentrations of polyamines (10 −3 M or less) give pictures which look like that obtained without polyamine, if fixation is followed by post-treatment with uranyl acetate. In such conditions, polyamines combine probably with DNA by intramolecular bonds. These intra- or inter-strand interactions within DNA molecules do not prevent their aggregation. The same result is obtained with calcium. Instead, uranyl cations bind irreversibly to DNA and enable visualization of individual molecules without intermolecular cross-links. With high concentrations, DNA molecules are linked by intermolecular bonds. The significance of the aggregation of DNA molecules by polyamines is discussed at the light of results obtained by biochemical methods.