Distribution of polypyrimidine . polypurine segments in DNA from diverse organisms

Polypyrimidine . polypurine segments are regions of duplex DNA which contain a highly asymmetric distribution of pyrimidine and purine nucleotides. A polypyrimidine in single-stranded DNA can be detected by its ability to form a complex and poly(A, G) which will bind to hydroxyapatite. We tested DNA from a variety of organisms and found that most contained polypyrimidines. From the shape of the curve relating DNA size to percentage bound to hydroxyapatite, we conclude that polypyrimidine . polypurine segments occur widely in DNA from higher organisms, at intervals of 6000--8000 base pairs throughout the majority of the genome. Lower levels occur in DNA from yeast and Drosophila.