Novel, sensitive assays for O6-alkylguanine and its repair and their application to studies of the molecular epidemiology of this lesion in human populations.

: Two assays suitable for monitoring human populations are presented--one for O6-alkylguanine-type adducts and one for the corresponding repair activity. The assay for adducts is based on competition for repair by O6-alkylguanine-DNA-alkyltransferase of lesions in the unknown DNA and in an oligonucleotide containing a single residue of O6-methylguanine (O6-meGua). The assay can reliably detect as little as 0.5 fmol O6-meGua or 3 fmol O6-ethylguanine in 10-15 micrograms DNA, and it has been used to measure O6-meGua (up to approximately 5 x 10(-7) mol/mol guanine) in lymphocyte DNA from individuals receiving procarbazine or dacarbazine. The assay for repair activity utilizes the same oligonucleotide as substrate for the enzyme, in combination with immunoprecipitation for convenient separation of repaired from unrepaired substrate. Examination of repair activity in biopsy specimens of gastric mucosa has revealed a correlation with the corresponding activity in lymphocytes (r = 0.7; p less than 0.01), indicating that lymphocytes could be used as surrogate markers for repair activity in gastric mucosa.