The influence of formamidopyrimidine-DNA glycosylase on the spontaneous and γ-radiation-induced mutation spectrum of the lacZα gene

• Published in: Mutation research. DNA repair 1999-10, Vol.435 (2), p.141-150
• Main Authors: Kuipers, Gitta K, Poldervaart, Hester A, Slotman, Ben J, Lafleur, M.Vincent M
• Format: Article
• Language: English
• Subjects: 8-dihydro-8-oxoguanine; Biological and medical sciences; Biological effects of radiation; formamidopyrimidine-DNA glycosylase; Fpg deficiency; Fpg protein; Fundamental and applied biological sciences. Psychology; Ionizing radiations; lacZ gene; M13; Molecular and cellular biology; Molecular genetics; Mutagenesis. Repair; Mutation spectrum; Tissues, organs and organisms biophysics; γ-Radiation
• ISSN: 0921-8777; 1386-1476
• DOI: 10.1016/S0921-8777(99)00043-9

Base excision repair (BER) is a very important repair mechanism to cope with oxidative DNA damage. One of the most predominating oxidative DNA damages after exposure to ionizing radiation is 7,8-dihydro-8-oxoguanine (8oxoG). This damage is repaired by formamidopyrimidine-DNA glycosylase (Fpg), a DNA glycosylase which is part of BER. Correct repair of 8oxoG is of great importance for cells, because 8oxoG has strong miscoding properties. Mispairing of 8oxoG with adenine instead of cytosine results in G:C to T:A transversion mutations. To determine the effect of a Fpg-deficiency on the spontaneous and γ-radiation-induced mutation spectrum in the lacZ gene, double-stranded (ds) M13 DNA, with the lacZα gene inserted as mutational target, was irradiated with γ-rays in aqueous solution under oxic conditions. Subsequently, the DNA was transfected into a wild-type Escherichia coli strain (JM105) and an isogenic Fpg-deficient E. coli strain (BH410). Although the overall spontaneous mutation spectra between JM105 and BH410 seemed similar, remarkable differences could be observed when the individual base pair substitutions were viewed. The amount of C to A transversions, which are most probably caused by unrepaired 8oxoG, has increased 3.5-fold in the spontaneous BH410 spectrum. When the γ-radiation-induced mutation spectra of JM105 and BH410 were compared, there was even a larger increase of C to A transversions in the BH410 strain (7-fold). We can therefore conclude that the straightforward approach used in this study confirms the importance of Fpg in repair of γ-radiation-induced damage, and most probably especially in the repair of 8oxoG.