Effect of Concentration on the Formation of Molecular Hybrids from T4 DNA

When the thymine of T4 DNA is replaced by 5-BU the melting temperature of T4 DNA is increased from about 83° to about 93°C. Heating and slow cooling of T4 DNA at concentrations of about 30μg/ml leads to aggregates which consist of several polynucleotide chains which appear in the electron microscope as a branched structure. The aggregates have regions which are true hybrids. When the concentration of T4 DNA is lowered to less than 1μg/ml the products of hybridization are not aggregates but have the morphology of native DNA molecules and the density labels are distributed as expected from the fusing of two chains of approximately equal length