DNA strand-break yields after post-irradiation incubation with base excision repair endonucleases implicate hydroxyl radical pairs in double-strand break formation.
OBJECTIVE
To determine the increases in SSB and DSB yields after post gamma-irradiation incubation of plasmid DNA with the Escherichia coli base excision repair endonucleases formamidopyrimidine-DNA N-glycosylase (FPG) and endonuclease III (endo III).


METHODS
Aqueous solutions of plasmid DNA were irradiated with 137Cs gamma-rays in the presence of 10(-4) - 10(-1) mol dm(-3) formate. After irradiation, aliquots were treated with FPG and/or endo III. SSB and DSB yields were then determined using gel electrophoresis.


RESULTS
Both SSB and DSB yields were found to increase after enzyme incubation, with the increase in the DSB yield being approximately equal to the square of the increase in the SSB yield. The correlation between the increases in the SSB and DSB yields was unaffected by the scavenger concentration during irradiation.


CONCLUSIONS
Under the conditions used, the majority of DSB appear to be formed from two hydroxyl radical attacks.
Milligan
J R
JR
Department of Radiology, University of California at San Diego, La Jolla, 92093-0610, USA. jmilligan@ucsd.edu
Aguilera
J A
JA
Nguyen
T T
TT
Paglinawan
R A
RA
Ward
J F
JF
D004247:DNA / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects*; D004249:DNA Damage; D004277:DNA, Single-Stranded / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D043382:DNA-Formamidopyrimidine Glycosylase; D043224:Deoxyribonuclease (Pyrimidine Dimer); D004706:Endodeoxyribonucleases / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology; D029968:Escherichia coli Proteins; D005561:Formates / Q000494:pharmacology; D016166:Free Radical Scavengers / Q000494:pharmacology; D005720:Gamma Rays; D017665:Hydroxyl Radical / Q000378:metabolism; D009699:N-Glycosyl Hydrolases / Q000378:metabolism; D010957:Plasmids / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects
D004277:DNA, Single-Stranded; D029968:Escherichia coli Proteins; D005561:Formates; D016166:Free Radical Scavengers; C030544:formic acid; D017665:Hydroxyl Radical; D004247:DNA; D004706:Endodeoxyribonucleases; D043224:Deoxyribonuclease (Pyrimidine Dimer); C106403:NTH protein, E coli; D009699:N-Glycosyl Hydrolases; D043382:DNA-Formamidopyrimidine Glycosylase; C468610:DNA-formamidopyrimidine glycosylase, E coli