Structure and mechanism of hydroxyl radical-induced formation of a DNA-protein cross-link involving thymine and lysine in nucleohistone.
Hydroxyl radical-induced formation of a DNA-protein cross-link involving thymine and lysine in calf thymus nucleohistone in vitro is reported. Basic amino acids such as lysine constitute a very high proportion of the amino acids of histones, and help histones to bind to DNA in chromatin. For this reason, basic amino acids are likely to participate in DNA-protein cross-linking. For identification of the thymine-lysine cross-link in nucleohistone, hydroxyl radical-induced cross-linking of thymine to lysine was investigated first using a model system, i.e., an aqueous mixture of thymine and lysine. Hydroxyl radicals were generated by exposure of this mixture to ionizing radiation after N2O saturation. The technique of gas chromatography-mass spectrometry was used to analyze the samples for possible cross-links. One thymine-lysine cross-link was found and its structure was elucidated. Using gas chromatography-mass spectrometry with selected-ion monitoring, this thymine-lysine cross-link was identified in acidic hydrolysates of calf thymus nucleohistone gamma-irradiated in N2O-saturated aqueous solution. The yield of this DNA-protein cross-link was also measured and found to be a linear function of radiation dose between 15 and 200 Gy. This yield amounted to 0.0085 mumol/J. Possible mechanisms for the formation of this DNA-protein cross-link in nucleohistone were proposed.
Dizdaroglu
M
M
Center for Chemical Technology, National Institute of Standards and Technology, Gaithersburg, Maryland 20899.
Gajewski
E
E
D000818:Animals; D002417:Cattle; D055598:Chemical Phenomena; D002621:Chemistry; D004247:DNA; D003852:Deoxyribonucleoproteins / Q000528:radiation effects; D005609:Free Radicals; D005720:Gamma Rays; D008401:Gas Chromatography-Mass Spectrometry; D006657:Histones; D006878:Hydroxides; D066298:In Vitro Techniques; D008239:Lysine; D013941:Thymine
D003852:Deoxyribonucleoproteins; D005609:Free Radicals; D006657:Histones; D006878:Hydroxides; D004247:DNA; D008239:Lysine; D013941:Thymine