Nuclease S1-mediated enhancement of the 32P-postlabeling assay for aromatic carcinogen-DNA adducts.

Treatment of DNA digests with nuclease P1 prior to 32P-labeling of adducts has previously been shown to enhance the sensitivity of the 32P-postlabeling assay for the detection of aromatic carcinogen-DNA adducts. The enhancement was based on the ability of nuclease P1 to remove the 3'-phosphate from normal nucleotides but not the corresponding phosphate from most aromatic adducted nucleotides. We investigated the utility of another 3'-dephosphorylating enzyme, nuclease S1, for this purpose, and found it to be as effective as nuclease P1. The recovery of DNA adducts derived from benzo[a]-pyrene (B[a]P), benzoquinone (BQ) and 2-acetylaminofluorene (AAF) was comparable after enhancement with either enzyme. Some differences were, however, observed. Recovery of a minor B[a]P adduct was 1.5 times higher by the S1 procedure. Among minor adducts of BQ, two showed higher values (2.8- and 6.1-fold) by the S1 procedure and one by the P1 procedure (2.4-fold). The major AAF adduct, deoxyguanosine-C8-AF, exhibited poorer recovery (1-11%) by either procedure, while the minor adducts, deoxyguanosine-N2-AAF and deoxyguanosine-C8-AAF, showed better recovery (2-3 times) than by the enhancement procedure involving extraction of adducts into butanol. Our results show that the nuclease S1 assay can complement the nuclease P1 assay, with improved recoveries for some adducts. Considering the complexity of the postlabeling assay, this additional variant may prove useful in unequivocal detection of DNA adducts.