Rapid
Histone-Catalyzed DNA Lesion Excision and Accompanying
Protein Modification in Nucleosomes and Nucleosome Core Particles
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Abstract
C5′-Hydrogen
atoms are frequently abstracted during DNA
oxidation. The oxidized abasic lesion 5′-(2-phosphoryl-1,4-dioxobutane)
(DOB) is an electrophilic product of the C5′-radical. DOB is
a potent irreversible inhibitor of DNA polymerase β, and forms
interstrand cross-links in free DNA. We examined the reactivity of
DOB within nucleosomes and nucleosome core particles (NCPs), the monomeric
component of chromatin. Depending upon the position at which DOB is
generated within a NCP, it is excised from nucleosomal DNA at a rate
275–1500-fold faster than that in free DNA. The half-life of
DOB (7.0–16.8 min) in NCPs is shorter than any other abasic
lesion. DOB’s lifetime in NCPs is also significantly shorter
than the estimated lifetime of an abasic site within a cell, suggesting
that the observed chemistry would occur intracellularly. Histones
also catalyze DOB excision when the lesion is present in the DNA linker
region of a nucleosome. Schiff-base formation between DOB and histone
proteins is detected in nucleosomes and NCPs, resulting in pyrrolone
formation at the lysine residues. The lysines modified by DOB are
often post-translationally modified. Consequently, the histone modifications
described herein could affect the regulation of gene expression and
may provide a chemical basis for the cytotoxicity of the DNA damaging
agents that produce this lesion