Sequence Specificity in the Interaction of the Four Stereoisomeric Benzo[c]phenanthrene Dihydrodiol Epoxides with the supF Gene

The shuttle vector pS189 was treated with each of the four configurational isomers of benzo[ c ]phenanthrene 3,4-dihydrodiol 1,2-epoxide, and the modified DNA was used as a template in a polymerase arrest assay examining the supF gene. Sites at which polymerase (Sequenase, version 2.0) progress along the template was blocked were presumed to be at or near sites of adduct formation. The polymerase arrest sites were compared with recently reported mutation hotspots induced by these agents in this gene (Bigger et al. , Proc. Natl. Acad. Sci. USA, 89: 368–372, 1992). For 31 of 32 mutation hotspots, a polymerase arrest band was present at or 1 or 2 nucleotides 3′- to that site, indicating that adduct formation tended to be associated with mutation hotspots. However, the arrest bands near mutation hotspots were not particularly prominent in all cases, and there were many sites of substantial polymerase arrest that were not in the vicinity of mutation hotspots. Thus, factors in addition to chemical selectivity must play key roles in determining sites of mutation.