Abasic sites preferentially form at regions undergoing DNA replication.
We investigated whether apurinic/apyrimidinic (AP/abasic) sites were more frequent in regions of DNA replication in cells and whether their number increased during oxidative stress. DNA fiber spreading and fluorescent immunostaining were used to detect areas of DNA replication and sites of AP lesions in extended DNA fibers. The distribution of AP sites was determined in DNA fibers from vertebrate cells maintained under normal culture conditions or stressed with exogenous H(2)O(2). AP lesions per unit length were enumerated in bulk DNA or at replication sites. The background density of AP sites in DNA fibers was 5.4 AP sites/10(6) nt, while newly replicated DNA contained 12.9 AP sites/10(6) nt. In cells exposed to 20 μM H(2)O(2), AP sites in newly replicated DNA increased to 20.8/10(6) nt. Determinations of AP site density in bulk DNA by fiber analysis or standard slot blot assays agreed to within 10%. Our findings show that the fiber assay not only accurately determines the frequency of AP sites but also shows their distribution. They also reveal that there is increased susceptibility to oxidative damage in DNA regions undergoing replication, which may explain the previously observed clustering of AP sites.
Department of Pathology and Laboratory Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7525, USA. pchastai@med.unc.edu
Paul D
PD
Chastain
Jun
J
Nakamura
Shangbang
S
Rao
Haitao
H
Chu
Joseph G
JG
Ibrahim
James A
JA
Swenberg
David G
DG
Kaufman
D000818:Animals; D002460:Cell Line; D002645:Chickens; D004249:DNA Damage; D004261:DNA Replication; D008856:Microscopy, Fluorescence; D017382:Reactive Oxygen Species / Q000378:metabolism
D017382:Reactive Oxygen Species