New methods for detection of low levels of DNA damage in human populations.

The use of a postlabeling method to characterize and to detect infrequent base modifications in DNA is outlined. This method has the advantage that low levels of DNA modifications, approximately 1 modified base per 10(5) nucleotides, can be detected. Moreover, a broad spectrum of modification can be identified by using this methodology. The basis for the method involves transfer of a radioactive phosphate from the gamma position of ATP to the 5'-hydroxyl terminus of 3'-phosphoryl nucleotides that are derived from modified DNA by appropriate nuclease digestion. The second method involves use of a defined DNA sequence within human cells. The alpha sequence is used as a probe for DNA damage to specific nucleotides. The alpha DNA sequence is reiterated approximately 300,000 times in the human genome and exists in tandem arrays. It comprises approximately 1% of the entire genome. The reiterated sequence is sufficiently homogeneous to permit its use as a probe for a site specific in DNA damage. Examples of the application of both of these methodologies to DNA damage inflicted in human cells by chemicals and ultraviolet light are provided.