- The biological activity of single-stranded phi X174 DNA, modified by N-hydroxy-2-aminofluorene, is inhibited by guanine imidazole ring-opening of the major, non-lethal aminofluorene-DNA adduct. Lutgerink, J.T., Retèl, J., Westra, J.G., Welling, M.C., Loman, H., Kriek, E. Carcinogenesis (1986)