RENATURATION AND ISOLATION OF SINGLE STRANDS FROM NUCLEAR DNA OF GUINEA PIG

Preparative density-gradient centrifugation in caesium chloride was used to separate guinea pig DNA into several fractions. As in the mouse, the satellite DNA region of the gradient was shown to contain the majority of the very rapidly renaturing sequences. The observed rate of renaturation, however, was nearly twice that of mouse satellite. The specificity of the reaction was demonstrated by showing that its rate was appropriately enhanced by the addition of denatured homologous DNA but not by denatured heterologous DNA. Centrifugation of satellite-enriched fractions in alkaline caesium chloride gradients revealed the presence of five distinct bands, of which four are thought to represent individual single strands of differing guanine plus thymine content. Two of these bands (α strands) were so widely separated that it was possible to isolate them directly without first preparing the satellite. Base composition, melting profiles, buoyant densities and behaviour on hydroxyapatite crystals indicate that the two α strands are complementary to each other. © 1969.