FRAMESHIFT MUTAGENESIS INDUCED IN ESCHERICHIA-COLI AFTER IN-VITRO TREATMENT OF DOUBLE-STRANDED DNA WITH METHYLENE-BLUE PLUS WHITE-LIGHT - EVIDENCE FOR THE INVOLVEMENT OF LESION(S) OTHER THAN 8-OXO-7,8-DIHYDRO-2'-DEOXYGUANOSINE

By means of specific mutation assays, we show here that in vitro treat ment of double-stranded plasmid DNA with methylene blue and white ligh t efficiently promotes frameshift mutagenesis in Escherichia coil. The assays detect either -1 or -2 frameshift mutations within previously characterized hot spot sequences for frameshift mutagenesis induced by the chemical carcinogen N-2-acetylaminofluorene, namely, short runs o f contiguous guanines and alternating GpC sequences, respectively. The SOS and umuDC dependences of these mutagenic processes have been inve stigated. Both -1 and -2 frameshift mutagenesis are increased when the host SOS functions are induced. However, and although functional UmuD C proteins are required for maximal mutation induction, the inducibili ty of both -1 and -2 frameshift mutagenesis is partially independent u pon the integrity of the umuDC operon. In addition, results obtained u sing plasmids with a site specifically located 7,8-dihydro-8-oxo-2'-de oxyguanosine (8-oxo-dGuo) residue show that this lesion, the major met hylene blue plus light induced lesion characterized so far, is ineffic ient in promoting frameshift mutagenesis. Together, these results led us to conclude that methylene blue plus light treatment of DNA induces , at relatively high rates, lesion(s) other than 8-oxo-dGuo, that effi ciently promote(s) frameshift mutagenesis in E. coil.