GREATER SUSCEPTIBILITY TO MUTATIONS IN LAGGING-STRAND OF DNA-REPLICATION IN ESCHERICHIA-COLI THAN IN LEADING-STRAND

Models of DNA replication in Escherichia coli involve an asymmetric DN A polymerase complex that replicates concurrently the leading and the lagging strands of double-stranded DNA. The effect of asymmetry on mut agenesis was tested with pairs of plasmids containing the unidirection al ColE1 origin of replication and a single lesion located in the lead ing or lagging strand. The lesion used was the covalent adduct that th e chemical carcinogen N-2-acetylaminofluorene (AAF) forms with the C-8 position of guanine. Whether SOS was induced or not, mutations arose at about a 20-fold higher frequency when the AAF adduct was located in the lagging strand than when in the leading strand.