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Oxidative Strand
Cleavage Initiated by Two Photon-induced Photoionization of Site-specifically
Incorporated 2-Aminopurine Residues in Oligonucleotides
Huang, Weidong 1,
Shafirovich, Vladimir1 and Geacintov, Nicholas1
New York University, New York, NY 100031
Abstract-
A 2-aminopurine (2AP) residue was site-specifically incorporated into
an 11-mer oligonucleotide 5'-CTCTC[2AP]CTTCC-3'(I) and duplexes
were formed with the complementary strand 5'-GGAAGTGAGAG-3'
(II). The duplexes were dissolved in aqueous buffer solutions and irradiated
with intense 308 nm XeCl excimer laser pulses under conditions that
are known to generate 2AP radicals, leading to strand cleavage at guanine
sites distant from the 2AP site (1). Strand cleavage in either strand
I or II was detected by high resolution polyacrylamide gel electrophoresis
and 32P 5'-end labeling of the DNA. The goals of these
studies were to compare the extent of cleavage on strands I and II before
("direct strand cleavage")
and after hot alkali treatment. In the 2AP-containing strand I, direct
cleavage occurred to approximately equal extents at all pyrimidine sites
and was, overall, four times more extensive than the cumulative cleavage
at all sites, including the guanines, on strand II. This suggests that
the reactive intermediates, generated by the photoionization of the
2AP, that initiate direct strand cleavage, migrate along and remain
predominantly on strand I. Hot alkali treatment enhances cleavage by
a factor of ~ 2 at the pyrimidines and 2AP in strand I, and by a factor
of ~ 4 at the guanines sites and the T opposite the 2AP residue in strand
II. The distribution of cleavage patterns on both DNA strands provide
new insights into the characteristics of photosensitized DNA strand
cleavage at a distance. (1) Shafirovich, V., Dourandin, A., Huang, W.,
Luneva, N. P., Geacintov, N. E., J. Phys. Chem. B 103
(49): 10924-10933.
Keywords: 2-aminopurine
, photoionization, DNA, damage
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