EFFECT OF UVM INDUCTION ON MUTATION FIXATION AT NON-PAIRING AND MISPAIRING DNA LESIONS

Mutation fixation at an ethenocytosine (EC) residue borne on transfect ed M13 single-stranded DNA is significantly enhanced in response to pr etreatment of Escherichia coli cells with UV, alkylating agents or hyd rogen peroxide, a phenomenon that we have called UVM for UV modulation of mutagenesis. The UVM response does not require the E. coli SOS or adaptive responses, and is observed in cells defective for oxyR, an ox idative DNA damage-responsive regulatory gene. UVM may represent eithe r a novel DNA-repair phenomenon, or an unrecognized feature of DNA rep lication in damaged cells that affects a specific class of non-coding DNA lesions. To explore the range of DNA lesions subject to the UVM ef fect, we have examined mutation fixation at 3,N-4-ethenocytosine and 1 ,N-6-ethenoadenine, as well as at O-6-methylguanine (O(6)mG). M13 vira l single-stranded DNA constructs bearing a single mutagenic lesion at a specific site were transfected into cells pretreated with UV or 1-me thyl-3-nitro-1-nitrosoguanidine (MNNG), Survival of transfected viral DNA was measured as transfection efficiency, and mutagenesis at the le sion site was analysed by a quantitative multiplex sequence analysis t echnology. The results suggest that the UVM effect modulates mutagenes is at the two etheno lesions, but does not appear to significantly aff ect mutagenesis at O(6)mG. Because the modulation of mutagenesis is ob served in cells incapable of the SOS response, these data are consiste nt with the notion that UVM may represent a previously unrecognized DN A damage-inducible response that affects the fidelity of DNA replicati on at certain mutagenic lesions in Escherichia coli.