ENDONUCLEASE-VII OF PHAGE-T4 NICKS N-2-ACETYLAMINOFLUORENE-INDUCED DNA STRUCTURES IN-VITRO

We have tested in vitro the activity of T4 endonuclease VII on three different double-stranded oligonucleotides bearing a single N-2-acetylaminofluorene (AAF) adduct covalently bound to each of the three guanine residues located within the NarI site (G(1)G(2)CG(3)CC), a strong frameshift mutation hot spot in E. coli. With the oligonucleotides modified at G(2) and G(3) a specific cleavage pattern with T4 endonuclease VII was observed in the complementary strand while no cleavage was found in the adduct-bearing strand. On the other hand, when G(1) modified, only a very faint cleavage band was observed (<1%). These differences in nicking among the three AAF-modified DNA substrates are discussed in terms of the polymorphic nature in adduct-induced DNA structures as previously shown. This ''non-physiological'' activity of a DNA resolvase is discussed in terms of a potential role for such enzymes in the induction of frameshift mutations.