SITE-SPECIFIC MUTAGENESIS BY A PROPANODEOXYGUANOSINE ADDUCT CARRIED ON AN M13 GENOME

The spectrum of mutations induced upon in vivo replication of an M13 g enome containing a site-specifically located propanodeoxyguanosine (Pd G) adduct was determined. PdG was used as a model for the major deoxyg uanosine adduct produced on reaction of DNA with the endogenous genoto xin malondialdehyde. PdG was introduced at position 6256 of M13MB102 b y ligating the oligodeoxynucleotide 5'-GGT(PdG)TCCG-3' into an 8-base gap in the (-)-strand of duplex M13MB102. Replication of the adducted strand was maximized by incorporation of uracil into the unadducted ()-strand. Following replication of dG-containing and PdG-containing M1 3MB102 genomes in Escherichia coli JM105, frameshift mutations were de tected as phenotypic changes in the lacZ(a) marker gene. Base pair sub stitutions were detected by differential hybridization using P-32-labe led 13-mers bearing different bases opposite position 6256. Neither fr ameshift nor base pair substitution mutations were detected following replication of PdG-adducted genomes in non-SOS-induced JM105. However, PdG --> T transversions and PdG --> A transitions were detected follo wing transformation of PdG-adducted M13MB102 into SOS-induced JM105. B oth types of mutations were detected at comparable frequencies, and th e total mutation frequency was approximately 2%. The results indicate that PdG is an efficient premutagenic lesion in E. coli strains in whi ch the SOS response is induced.