Abstract
The analysis by CsCl density gradient of nucleolar DNA has revealed that the 1.700 g/cm3 main component can be subdivided in three subcomponents with buoyant densities of 1.707 g/cm3, 1.700 g/cm3, 1.690 g/cm3. The 1.707 g/cm3 and 1.690 g/cm3 components contain all the repetitive sequences which comprise 15 % of the total nucleolar DNA. The ribosomal cistrons are found in components having buoyant density between 1.707 g/cm3 and 1.725 g/gm3. Sodium-p-aminosalicylate-DNA interactions have revealed that only the 1.700 g/cm3 fraction has a destabilized secondary structure. The possible localization of these different fractions on peri and intranucleolar fractions is discussed.