SOS-dependent A -> G transitions induced by hydroxyl radical generating system hypoxanthine xanthine oxidase/Fe3+/EDTA are accompanied by the increase of Fapy-adenine content in M13 mp18 phage DNA
Ma. Graziewicz et al., SOS-dependent A -> G transitions induced by hydroxyl radical generating system hypoxanthine xanthine oxidase/Fe3+/EDTA are accompanied by the increase of Fapy-adenine content in M13 mp18 phage DNA, MUT R-DNA R, 434(1), 1999, pp. 41-52
Gas chromatography/isotope dilution-mass spectrometry with selected ion mon
itoring (GC/IDMS-SIM) was used to measure oxidised bases in hypoxanthine/xa
nthine oxidase/Fe3+/EDTA modified ss M13 mp18 phage DNA. A dose-dependent i
ncrease of oxidised bases content in DNA was observed with the biggest augm
entation of FapyGua, thymine glycol and FapyAde, The amount of 8-OH-Gua was
relatively high both in non-oxidised and oxidised DNA, and increased to th
e same extent as FapyAde and ThyGly. DNA oxidation caused a dramatic decrea
se in phage survival after transfection to E, coli. Survival was improved 2
.8-fold after induction of the SOS system by UV irradiation of bacteria and
mutation frequency of the lacZ gene in SOS conditions increased 7-fold ove
r that in non-irradiated bacteria. Spectrum of mutations was different from
those reported previously and mutations were distributed rather randomly w
ithin M13 lacZ sequence, which was in contrast to previous findings, where
with non-chelated metal ions other types of mutations were found in several
clusters. Thus, conditions of DNA oxidation and accessibility of metal ion
s for DNA bases might be important factors for generating different DNA dam
ages and mutations. Major base substitutions found both in SOS-induced and
non-induced E, coli but with higher mutation frequency in SOS-induced cells
were C --> A (similar to 20-fold increase in SOS-conditions), G --> A (9-f
old increase) and G --> C (4.5-fold increase). Very few G --> T transitions
were found. A particularly large group of A --> G transitions appeared onl
y in SOS-induced bacteria and was accompanied by augmentation of FapyAde co
ntent in the phage DNA with undetectable 2-OH-Ade. It is then possible that
imidazole ring-opened adenine mimics guanine during DNA replication and pa
irs with cytosine yielding A --> G transitions in SOS-induced bacteria. (C)
1999 Elsevier Science B.V. All rights reserved.