Deoxyinosine (dI) in DNA can arise from hydrolytic or nitrosative deamination of deoxyadenosine It is excised in a -repair pathway that is initiated by endonuclease V. the nfi gene product, in Escherichia col: Repair was studied in vitro using M13mp18 derived heteroduplexes containing a site -specific deoxyinosine Unpaired dI/G mismatch resides within the recognition site for Xhol restriction endonucleases, permitting evaluation of repair occurring on deoxyinosine- containing DNA strand Our results show that dI lesions were efficiently repaired in nfi(+) E coli extracts but the repair level was much reduced in nfi mutant extracts We subjected the deoxyinosine-containing heteroduplex to a purified system consisting of soluble endonuclease V fusion protein. DNA polymerase I. and DNA ligase, along with the four deoxynucleoside triphosphates Interestingly we found these three proteins alone are sufficient to process the dI lesion efficiently We also found that the 3'-exonuclease activity of DNA polymerase I is sufficient to remove the dI lesion in this minimum reconstituted assay ; 醫學檢驗暨生物技術學系 ; 醫學院 ; 期刊論文