Adenine plus thymine and guanine plus cytosine enriched fractions of animal DNA's as indicators of polynucleotide homologies

Double-stranded animal DNA fragments, sheared in a pressure cell (mol. wt about 400,000 daltons), were fractionated according to base composition by isopycnic sedimentation in cesium chloride. Hybridization experiments were performed with radiolabeled, fractionated, AT- or GC-rich DNA fragments and unlabeled competitor DNA's from several animal sources. Among animals sharing common polynucleotide sequences, greater homology could be demonstrated with the GC-rich DNA fragments than with the AT-rich fraction. The greater specificity of the AT-rich DNA for homologous polynucleotide sequences persisted over the temperature range 50 to 72 °C, becoming more marked at higher incubation temperatures.