Dehydration, deamination and enzymatic repair of cytosine glycols from oxidized poly(dG-dC) and poly(dI-dC).
Cytosine glycols (5,6-dihydroxy-5,6-dihydrocytosine) are initial products of cytosine oxidation. Because these products are not stable, virtually all biological studies have focused on the stable oxidation products of cytosine, including 5-hydroxycytosine, uracil glycols and 5-hydroxyuracil. Previously, we reported that the lifetime of cytosine glycols was greatly enhanced in double-stranded DNA, thus implicating these products in DNA repair and mutagenesis. In the present work, cytosine and uracil glycols were generated in double-stranded alternating co-polymers by oxidation with KMnO4. The half-life of cytosine glycols in poly(dG-dC) was 6.5 h giving a ratio of dehydration to deamination of 5:1. At high substrate concentrations, the excision of cytosine glycols from poly(dG-dC) by purified endonuclease III was comparable to that of uracil glycols, whereas the excision of these substrates was 5-fold greater than that of 5-hydroxycytosine. Kinetic studies revealed that the V(max) was several fold higher for the excision of cytosine glycols compared to 5-hydroxycytosine. In contrast to cytosine glycols, uracil glycols did not undergo detectable dehydration to 5-hydroxyuracil. Replacing poly(dG-dC) for poly(dI-dC) gave similar results with respect to the lifetime and excision of cytosine glycols. This work demonstrates the formation of cytosine glycols in DNA and their removal by base excision repair.
Tremblay
Sébastien
S
Department of Nuclear Medicine and Radiobiology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Québec, Canada.
Wagner
J Richard
JR
D003596:Cytosine / Q000031:analogs & derivatives* / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D004260:DNA Repair; D045643:DNA Repair Enzymes / Q000378:metabolism*; D043382:DNA-Formamidopyrimidine Glycosylase / Q000378:metabolism; D003641:Deamination; D043224:Deoxyribonuclease (Pyrimidine Dimer) / Q000378:metabolism; D007700:Kinetics; D010084:Oxidation-Reduction; D011089:Polydeoxyribonucleotides / Q000737:chemistry* / Q000378:metabolism; D011196:Potassium Permanganate / Q000737:chemistry; D014498:Uracil / Q000031:analogs & derivatives / Q000032:analysis
D011089:Polydeoxyribonucleotides; C111900:uracil glycol; D011196:Potassium Permanganate; C049744:cytosine glycol; C031156:poly d(I-C); C019530:poly(dC-dG); D014498:Uracil; D003596:Cytosine; D043224:Deoxyribonuclease (Pyrimidine Dimer); D043382:DNA-Formamidopyrimidine Glycosylase; D045643:DNA Repair Enzymes