IN SEARCH OF A MUTATIONAL HOTSPOT

In vitro selection was used to define sequence contexts that significa ntly enhanced the mutagenic potential of 7,8-dihydro-8-oxoguanine (8-o xoG). Contexts that simultaneously reduced the efficiency of 8-oxoG cl eavage by formamidopyrimidine DNA N-glycosylase and increased the effi ciency of misincorporating A opposite the lesion by DNA polymerase wer e isolated from a pool of 4(8) random octanucleotide sequences. Kineti c analysis showed that the combined effects of poor repair and high mi scoding resulted in 10(2)- to 10(3)-fold increase in the mutagenic pot ential of 8-oxoG. Furthermore, the isolated sequence contexts correlat ed strongly with G --> T transversion hotspots in spontaneous mutation al spectra reported for the Escherichia coil lad and human p53 and fac tor LY genes. We present an example directly linking the interplay bet ween DNA repair and replication to a ''high risk sequence'' for base s ubstitution.