Efficient and accurate bypass of N 2 -(1-carboxyethyl)-2′-deoxyguanosine by DinB DNA polymerase in vitro and in vivo

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Abstract
DinB, a Y-family DNA polymerase, is conserved among all domains of life; however, its endogenous substrates have not been identified. DinB is known to synthesize accurately across a number of N 2 -dG lesions. Methylglyoxal (MG) is a common byproduct of the ubiquitous glycolysis pathway and induces the formation of N 2 -(1-carboxyethyl)-2′-deoxyguanosine ( N 2 -CEdG) as the major stable DNA adduct. Here, we found that N 2 -CEdG could be detected at a frequency of one lesion per 10 7 nucleosides in WM-266-4 human melanoma cells, and treatment of these cells with MG or glucose led to a dose-responsive increase in N 2 -CEdG formation. We further constructed single-stranded M13 shuttle vectors harboring individual diastereomers of N 2 -CEdG at a specific site and assessed the cytotoxic and mutagenic properties of the lesion in wild-type and bypass polymerase-deficient Escherichia coli cells. Our results revealed that N 2 -CEdG is weakly mutagenic, and DinB (i.e., polymerase IV) is the major DNA polymerase responsible for bypassing the lesion in vivo . Moreover, steady-state kinetic measurements showed that nucleotide insertion, catalyzed by E. coli pol IV or its human counterpart (i.e., polymerase κ), opposite the N 2 -CEdG is both accurate and efficient. Taken together, our data support that N 2 -CEdG, a minor-groove DNA adduct arising from MG, is an important endogenous substrate for DinB DNA polymerase.

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