Albany 2013: Book of Abstracts

category image Albany 2013
Conversation 18
June 11-15 2013
©Adenine Press (2012)

Activity of DNA Ligase on Substrates Containing Non-canonical Structures

The expansion of trinucleotide repeat tracts (e.g. (CAG)n tracts) has been shown to contribute to genomic instability and has been implicated in the pathogenesis of several neurodegenerative diseases, including Huntington’s Disease and Fragile X syndrome (Kovtun et al, 2008). While the molecular mechanism of this expansion is unknown, the ability of trinucleotide repeat sequences to form non-canonical secondary structures, such as hairpins, has been implicated as a multifaceted source of error (Gacy et al, 1995). Non-canonical DNA secondary structures have been shown to impact the action of enzymes in the base excision repair (BER) pathway, by which oxidatively damaged bases are removed. More specifically, there is evidence that trinucleotide repeat-containing DNA mistakenly enters long-patch BER, which can potentially lead to the incorporation of extra nucleobases by DNA polymerase (Jarem et al, 2011). The final enzyme in the BER pathway is DNA Ligase, which catalyzes the formation of a phosphodiester bond to seal a nick site (Taylor et al, 2011). When extra nucleotides have been added during an erroneous long-patch BER process, the action of DNA ligase may expand the repeat tract by incorporating these additional bases into duplex DNA. In this study, DNA constructs containing (CAG)n hairpins at various distances from a nick site are used to investigate the ability of DNA Ligase to ligate substrates containing non-canonical secondary structure back into duplex DNA.

This research has been supported by National Institute of Environmental Health Sciences (R01ES019296).


  1. Gacy, A.M., Goellner, G., Juranic, N., Macura, S., McMurray, C. T. (1995) Trinucleotide repeats that expand in human disease form hairpin structures in vitro. Cell, 81, 533-540
  2. Jarem, D., Wilson, N.R., Schermerhorn, K.M., Delaney, S. (2011)
  3. Incidence and persistence of 8-oxo-7,8-dihydroguanine within a hairpin intermediate exacerbates a toxic oxidation cycle associated with trinucleotide repeat expansion. DNA Repair, 10, 887-896
  4. Kovtun, I.V., McMurray, C.M. (2008) Features of trinucleotide repeat instability in vivo. Cell Res., 18, 198-213
  5. Taylor, M.R., Conrad, J.A., Wahl, D., O’Brien, P.J. (2011) Kinetic Mechanism of Human DNA Ligase I Reveals Magnesium-dependent Changes in the Rate-Limiting Step That Compromise Ligation Efficiency. J. Biol. Chem., 286, 23054-23062

Katharina Bilotti
Kelly Schermerhorn
and Sarah Delaney

Department of Chemistry Brown University Providence, RI 02906

Ph: (401) 863-2044
Fx: (401)863-1993
Email: katharina_bilotti@brown.edu