Nucleic Acids Research, Vol 24, Issue 11 1987-1991, Copyright © 1996 by Oxford University Press
H Brunar and PB Dervan
A nonnatural nucleoside, 7-(2-deoxy-beta-D-erythro-pento-furanosyl)-
guanine (d7G), mimics protonated cytosine and specifically binds GC base
pairs within a pyrimidine - purine - pyrimidine triple helix. The
differences in association constants (KT) determined by quantitative
footprint titration experiments at neutral pH reveal dramatic sequence
composition effects on the energetics of triple helix formation by
oligonucleotides containing d7G. Purine tracts of sequence composition
5'-d(AAAAAGAGAGAGAGA)-3' are bound by oligonucleotide 5'-
d(TTTTT7GT7GT7GT7GT7GT)-3' three orders of magnitude less strongly than by
5'-d(TTTTTmCTmCTmCTmCTmCT)-3' (KT = 1.5 x 10(6) M(-1) and KT > or = 3 x
10(9) M(-1) respectively). Conversely, purine tracts of sequence
composition 5'-d(AAAAGAAAAGGGGGGA)-3' are bound by oligonucleotide 5'-
d(TTTTmCTTTT7G7G7G7G7G7GT)-3' five orders of magnitude more strongly than
by 5'-d(TTTTmCTTTTmCmCmCmCmCT)-3' (KT > or = 3 x 10(9) M(-1) and KT <
5 x 10(4) M(-1) respectively). The complementary nature of d7G and mC
expands the repertoire of G-rich sequences which may be targeted by triple
helix formation.
ARTICLES
Sequence composition effects on the stabilities of triple helix formation by oligonucleotides containing N7-deoxyguanosine
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA.
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