Restriction enzyme mapping of carcinogen binding regions on pBR322

Previous equilibrium binding experiments (S.A. Winkle and T.R. Krugh, Nucleic Acids Res. 9, 3175-3186 (1981)) suggested that the carcinogen N-hydroxy-N-acetyl-2-aminofluorene might exhibit preferential binding to a small number of sites on phiX174 DNA. To examine whether the covalently binding analogue N-acetoxy-N-acetyl-2-aminofluorene (acetoxyAAF) also possesses high affinity sites, the plasmid pBR322 was reacted with 3H labeled acetoxyAAF to give one to sixteen adducts per DNA molecule. Thus only higher affinity sites would be affected. The DNA was subsequently cleaved with either Alu I, Hae III, Hha I, Hinf I or Hpa II restriction endonuclease and the restriction fragments isolated by gel electrophoresis. Examination of the distribution of 3H acetoxyAAF among the fragments was not random but, rather, with each enzyme, the acetoxyAAF was found predominantly in a few fragments. The locations of the bands containing the acetoxyAAF for each enzyme overlap--suggesting that there are regions on pBR 322 which contain high affinity sites for acetoxyAAF binding.