DNA MUTAGENESIS AND REPAIR IN UV-IRRADIATED ESCHERICHIA-COLI K-12 UNDER CONDITION OF MUTATION FREQUENCY DECLINE

This paper shows that mutation frequency decline (MFD) occurs in UV-ir radiated and transiently starved Escherichia coli K-12 strain AB1157. This effect involves preferential repair of pre-mutagenic lesions situ ated on the transcribed strand, and is mfd-, and uvrA-dependent. Mutat ions were tested by measuring reversion of argE3((ochre)) to Arg(+) an d the types of reversions and the mutational specificity were defined. UV-irradiation induces reversions to Arg(+) predominantly by forming ochre suppressors, supB and, much more rarely, supE((ochre)). In irrad iated and then transiently starved cells, the ratio of supB/supE((ochr e)) is reversed, and supE((ochre)) suppressors predominate. Back rever sions at the argE3 site occurs only in bacteria defective in UvrABC-ex cinuclease. The introduction of a Tn10 transposon makes bacteria more sensitive to UV-irradiation and diminishes the frequency of reversions . Transformation with pCW2123, a umuD'C-bearing plasmid, recovers and enhances the frequency of reversion but has no effect on post-UV-survi val of the bacteria. (C) 1998 Elsevier Science B.V. All rights reserve d.