Effect of aminofluorene and (acetylamino)fluorene adducts on the DNA replication mediated by Escherichia coli polymerases I (Klenow fragment) and III.

N-(Deoxyguanosin-C8-yl)-2-(acetylamino)fluorene (dG-C8-AAF) and N-(deoxyguanosin-C8-yl)-2-aminofluorene (dG-C8-AF) are the two major DNA adducts induced by the chemical carcinogen 2-(acetylamino)fluorene (AAF). Molecular modeling shows that, in the DNA double helix, dG-C8-AF can maintain an anti-structure and normal base pairing, while dG-C8-AAF favors a syn-structure and causes base displacement. In the phi X174 RF DNA-Escherichia coli transfection system, it has been found that dG-C8-AF is 7-10-fold less lethal than dG-C8-AAF; these results suggest that these two kinds of DNA adducts may have different effects on DNA replication and that they may be repaired by different pathways. We have investigated the effects of these two kinds of adducts on DNA polymerase III holoenzyme (pol III-H) and DNA polymerase I Klenow fragment (pol I-Kf) mediated DNA synthesis by using carcinogen-modified M13 single-stranded DNA hybridized with 32P-labeled primer as templates. We have found that pol III-H and pol I-Kf replicate through dG-C8-AF with 92% and 62% frequency, respectively; in contrast, these two enzymes replicate through dG-C8-AAF with only 38% and 25% frequency, respectively. AF-adducted DNA shows a more profound sequence specificity in blocking DNA synthesis than AAF-adducted DNA, and the sequence specificities in blocking DNA synthesis for both kinds of adducts differ for pol III-H and pol I-Kf.