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Book of Abstracts: Albany 2011

category image Albany 2011
Conversation 17
June 14-18 2011
©Adenine Press (2010)

Incorporation of Oxidized Guanine Nucleotides into DNA

An oxidized product of guanine that is detected following exposure of DNA to one of several oxidizing agents is 8-oxo-7,8-dihydro-guanine (8-oxoGua). 8-oxoGua is present in genomic DNA at steady-state levels of ~1-10 per 107 bases and is a biomarker for several diseases (1). In order to prevent the genetic effects caused by the presence of 8-oxoGua, cells are equipped with several repair enzymes. Mammalian cells have a glycosylase/AP lyase, OGG1 (MutM in E. coli), that excise 8-oxoGua from duplex DNA when it is paired with cytosine. A second glycosylase, MYH (MutY in E. coli), removes adenine from an OG:A mispair. Cells are also equipped with a phosphatase, MTH1 (MutT in E. coli), that can convert 8-oxodGuoTP to 8-oxodGuoMP; this action removes 8-oxodGuoTP from the nucleotide pool in order to prevent incorporation during DNA replication. The importance of removing 8-oxodGuoTP from the nucleotide pool is underscored by the fact that E. colilacking MutT, have a 100-10,000-fold higher mutation rate compared to wild type E. coli (2,3). This dramatic increase in mutation rate in the absence of MutT indicates that the nucleotide pool represents a biologically significant source of 8-oxoGua. Indeed, the incorporation of 8-oxodGuoTP by several bacterial and mammalian polymerases has been examined (4,5). Not only has 8-oxoGua been shown to be mutagenic when replicated in DNA, it has also been shown to be chemically labile towards further oxidation (6,7). Several oxidized 8-oxoGua lesions have been identified such as spiroiminodihydantoin and guanidinohydantoin. Many of these oxidized lesions have been shown to be potently toxic and mutagenic when replicated in vitro and in vivo. The aim of this investigation is to determine the extent to which the nucleotide pool serves as a source of these oxidized lesions and their ability to be substrates for DNA polymerases.

References

  1. H. J. Helbock, K.B. Beckman, M.K. Shigenaga, P. Walter, A.A. Woodall, H.C. Yeo, and B. N. Ames, Proc. Natl. Acad. Sci. USA, 95, 288-293 (1998).
  2. H. Maki and M. Sekiguchi, Nature, 355, 273–275 (1992).
  3. M. L. Michaels, C. Cruz, A.P. Grollmam, and J. H. Miller, Proc Natl. Acad. Sci. USA., 89, 7022–7025 (1992).
  4. H. J. Einolf, N. Schnetz-Boutaud, and P. F. Geungerich, Biochemistry, 37, 13300–13312 (1998).
  5. J. W. Hanes, D.M. Thal, D. M., and K. A. Johnson, J. Biol. Chem., 281, 36241-36248 (2006).
  6. W. L. Neeley and J.M. Essigmann, Chem. Res. Toxicol., 19, 491-505 (2006).
  7. J. C. Niles, J. S. Wishnok, and S. R. Tannenbaum, Nitric Oxide, 14, 109-121(2006).

Craig J. Yennie
Sarah Delaney

Department of Chemistry
Brown University
Providence, RI 02912 USA

Ph: (401) 863-2055
Fx: (401) 863-9368
craig_yennie@brown.edu