posted on 2016-09-09, 00:00authored byNicole
L. Williams, Pengcheng Wang, Yinsheng Wang
DNA
alkylation represents a major type of DNA damage and is generally
unavoidable due to ubiquitous exposure to various exogenous and endogenous
sources of alkylating agents. Among the alkylated DNA lesions, O2-alkylthymidines (O2-alkyldT) are known to be persistent and poorly repaired in mammalian
systems and have been shown to accumulate in the esophagus, lung,
and liver tissue of rats treated with tobacco-specific N-nitrosamines, i.e., 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone
(NNK) and N′-nitrosonornicotine (NNN). In
this study, we assessed the replicative bypass of a comprehensive
set of O2-alkyldT lesions, with the alkyl
group being a Me, Et, nPr, iPr, nBu, iBu, or sBu, in template
DNA by conducting primer extension assays with the use of major translesion
synthesis DNA polymerases. The results showed that human Pol η
and, to a lesser degree, human Pol κ, but not human polymerase
ι or yeast polymerase ζ, were capable of bypassing all O2-alkyldT lesions and extending the primer to
generate full-length replication products. Data from steady-state
kinetic measurements showed that human Pol η exhibited high
frequencies of misincorporation of dCMP opposite those O2-alkyldT lesions bearing a longer straight-chain alkyl
group. However, the nucleotide misincorporation opposite branched-chain
lesions was not selective, with dCMP, dGMP, and dTMP being inserted
at similar efficiencies, though the total frequencies of nucleotide
misincorporation opposite the branched-chain lesions differed and
followed the order of O2-iPrdT > O2-iBudT > O2-sBudT. Together, the results
from the present study provided important knowledge about the effects
of the length and structure of the alkyl group in the O2-alkyldT lesions on the fidelity and efficiency of DNA
replication mediated by human Pol η.