Figure 6.

Susceptibility of εG lesions to AlkB repair in vitro. (A) Mass spectra of 16-mer oligonucleotides containing either a 2′-F-N²,3-εG, 1,N²-εG or 2′-F-1,N²-εG following 1 h incubation with AlkB. Data represent the −4 charge envelopes and the observed monoisotopic peak value is labeled above each peak envelope. (B) The proposed mechanism of AlkB repair on (2′-F-)1,N²-εG. Theoretical m/z values of the −4 charged ions of the 16-mer oligonucleotides starting materials, putative reaction intermediates and repair products are listed for both the 2′-deoxy (2′-H) and 2′-fluoro (2′-F) versions of the bases. A recent theoretical study proposed that repair of εA by AlkB may be mediated by a zwitterionic species, and that some of the species observed by the MS analysis could be byproducts rather than repair intermediates (56). However, the ability of AlkB to repair the εG lesions is not affected by this hypothesis.