Related single copy sequences in the human genome.

Human single copy DNA renatured under relatively non-stringent conditions (50 degrees C, 0.36 M Na+) forms two components with different thermal stabilities: a high temperature component melting at a temperature (81 degrees C, 0.18 M Na+) expected for well-paired duplex and a low temperature component melting at 55 degrees C (0.18 M Na+). The production of the high and low temperature components has been examined as a function of C0t (product of concentration and time in units of mol/s per l) value and renaturation temperature. The duplex formed has been characterized by its resistance to S1 endonuclease and its length has been determined by gel electrophoresis. As a result of these experiments and related controls we conclude that the low temperature component is not an artifact of DNA fragment length, nonspecific base pairing or hydroxyapatite chromatography conditions. We attribute the low thermal stability of this component to the renaturation of distantly related single copy sequences to form a highly mismatched duplex DNAs with an average length of about 100 base pairs.