Nucleic Acids Research, Vol 24, Issue 24 5013-5020, Copyright © 1996 by Oxford University Press
I Mukerji, MC Shiber, JR Fresco and TG Spiro
The structure of the oligonucleotide d(A-G)10 in 0.6 M Na+, pH 7.0 has been
investigated with UV resonance Raman (UVRR) spectroscopy. Variable
wavelength excitation was used to distinguish the spectral contributions of
dG and dA residues. Both classes of residues show UVRR hyperchromism with
increasing temperature, reflecting unstacking of the bases. The dG residues
melt relatively cooperatively with a Tm of approximately 42 degrees C.
Unstacking is non-cooperative for the dA residues, increasing linearly
between 4 and 80 degrees C. G-tetrads at low temperature are indicated by
UVRR frequency shifts of modes associated with C6=O and C2-NH2 of the dG
residues, and of vibrations involving N7, all sites of H-bonding. However,
there are no indications of interbase H-bonds for the dA residues, showing
they do not form H- bonded tetrads. Most of the bases are oriented anti
about the glycosyl bond, but at 4 degrees C a fraction of the residues are
syn. These results, together with the findings by Shiber et al.
[Shiber,M.C., Braswell,E.H., Klump,H. and Fresco,J.R. (1996) Nucleic Acids
Res. 24, 5004-5012] that d(A-G)10 under comparable conditions has the
molecular weight of a dimer, support a model in which two hairpins interact
to form a helical structure with G-tetrads and intercalated dA residues.
ARTICLES
A UV resonance Raman study of hairpin dimer helices of d(A-G)10 at neutral pH containing intercalated dA residues and alternating dG tetrads
Department of Chemistry, Princeton University, NJ 08544-1014, USA.
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