Nucleic Acids Research, Vol 24, Issue 4 586-595, Copyright © 1996 by Oxford University Press
S Nonin, JL Leroy and M Gueron
Acid-induced catalysis of imino proton exchange in G.C pairs of DNA
duplexes is surprisingly fast, being nearly as fast as for the isolated
nucleoside, despite base-pair dissociation constants in the range of 10(-5)
at neutral or basic pH. It is also observed in terminal G.C pairs of
duplexes and in base pairs of drug-DNA complexes. We have measured imino
proton exchange in deoxyguanosine and in the duplex (ATATAGATCTATAT) as a
function of pH. We show that acid-induced exchange can be assigned to
proton transfer from N7-protonated guanosine to cytidine in the open state
of the pair. This is faster than transfer from neutral guanosine (the
process of intrinsic catalysis previously characterized at neutral ph) due
to the lower imino proton pK of the protonated form, 7.2 instead of 9.4.
Other interpretations are excluded by a study of exchange catalysis by
formiate and cytidine as exchange catalysts. The cross-over pH between the
regimes of pH-independent and acid-induced exchange rates is more basic in
the case of base pairs than in the mononucleoside, suggestive of an
increase by one to two decades in the dissociation constant of the base
pair upon N7 protonation of G. Acid-induced catalysis is much weaker in A.T
base pairs, as expected in view of the low pK for protonation of thymidine.
ARTICLES
Acid-induced exchange of the imino proton in G.C pairs
Groupe de Biophysique de l'Ecole Polytechnique et de l'URA 1254 du CNRS, 91128 Palaiseau, France.
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  L. Jiang and I. M. Russu Proton exchange and local stability in a DNA triple helix containing a G.TA triad Nucleic Acids Res., October 15, 2001; 29(20): 4231 - 4237. [Abstract] [Full Text] [PDF]
|
|