PROOFREADING-DEFECTIVE DNA-POLYMERASE-II INCREASES ADAPTIVE MUTATION IN ESCHERICHIA-COLI

The role of Escherichia coli PNA polymerase (Pol) II in producing or a voiding mutations was investigated by replacing the chromosomal Pol II gene (polB(+)) by a gene encoding an exonuclease-deficient mutant pol II (polBex1). The polBex1 allele increased adaptive mutations on an e pisome in nondividing cells under lactose selection. The presence of a Pol III antimutator allele (dnaE915) reduced adaptive mutations in bo th polB(+) cells and cells deleted for polB (polB Delta 1) to below th e wild type level, suggesting that both Pol II and pol III are synthes izing episomal DNA in nondividing cells but that in wild-type cells Po l III generates the adaptive mutations'. The adaptive mutations were m ainly -1 frameshifts occurring in short homopolymeric runs and were si milar in wild-type, polB Delta 1, and polBex1 strains. Mutations produ ced by both Pol III and Pol II ex1 were corrected by the mutHLS mismat ch repair system.