Uracil-DNA glycosylase produces excess lethal damage induced by an Auger cascade in BrdU-labelled bacteriophage T1.
T1 phages with and without 5-bromo-2'-deoxyuridine (BrdU) labelling were irradiated in solids with monochromatic X-rays at 12.40 and 13.51 keV, below and just above the K-absorption edge of bromine (13.47 keV) in vacuum and wet states. Irradiated phages were assayed on uracil-DNA glycosylase (Udg) deficient (ung-1) and sufficient (ung+) host strains of Escherichia coli, in order to investigate the nature of the lethal damage induced by Auger cascade following X-ray absorption at the K-shell of bromine as a key atom. The results were: (1) An Auger-specific enhancement (1.15) was observed only when BrdU-labelled phages were irradiated in the wet state and assayed on ung+ host cells. (2) A Udg-specific enhancement was observed only for BrdU-labelled phages, not for unlabelled phages. (3) The sensitivities of BrdU-unlabelled phages were almost the same, despite the irradiation states and strains of the host cell, indicating that this sensitivity was a common fraction of the sensitivity under all conditions. (4) The lethal damage for the T1 phage was categorized into four fractions according to the sensitivities under different conditions: the general fraction was defined as being the sensitivity of unlabelled phages (G-fraction); BrdU-specific, but unrecognizable by Udg (B-fraction); Udg specific, but not Auger-specific (U-fraction); and Auger-specific (A-fraction). (5) Although the so-called indirect action of water radicals increased only the G-fraction by about three-fold, the B- and U-fractions were not affected by any change in the irradiation states, thus indicating that these two fractions were caused by the so-called direct action.
Furusawa
Y
Y
Department of Molecular Biology, Tokai University School of Medicine, Kanagawa, Japan.
Maezawa
H
H
Suzuki
K
K
Yamamoto
Y
Y
Kobayashi
K
K
Hieda
K
K
D000345:Affinity Labels; D001966:Bromine / Q000494:pharmacology; D001973:Bromodeoxyuridine; D004249:DNA Damage; D045647:DNA Glycosylases; D004260:DNA Repair; D004307:Dose-Response Relationship, Radiation; D005814:Genes, Viral; D009699:N-Glycosyl Hydrolases / Q000494:pharmacology*; D013604:T-Phages / Q000528:radiation effects*; D051981:Uracil-DNA Glycosidase; D014965:X-Rays
D000345:Affinity Labels; D045647:DNA Glycosylases; D009699:N-Glycosyl Hydrolases; D051981:Uracil-DNA Glycosidase; D001973:Bromodeoxyuridine; D001966:Bromine