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Base tilt of B-form poly[d(G)]-poly[d(C)] and the B- and Z-conformations of poly[d(GC)]-poly[d(GC)] in solution

✍ Scribed by Stephen P. Edmondson; W. Curtis Johnson Jr.

Publisher: Wiley (John Wiley & Sons)
Year: 1986
Tongue: English
Weight: 785 KB
Volume: 25
Category: Article
ISSN: 0006-3525
DOI: 10.1002/bip.360251211

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✦ Synopsis

We have measured the CD, isotropic absorption, and linear dichroism (LD) in the vacuum-uv spectral region for the B-conformations of poly[d(G)]-poly[d(C)] and poly[d(GC)]-poly[d(GC)],

and for the 2-conformation of poly[d(GC)]-poly[d(GC)] formed in 70% trifluoroethanol. The reduced dichroism (LD divided by isotropic absorption) for all conformations varied with wavelength, indicating that the bases are not perpendicular to the helix axis. Since the directions of the transition dipoles are known, the inclinations and axes of inclination of each base can be determined from the wavelength dependence of the reduced dichroism spectra. The results indicate that the base normals of the (G + C) polymers in the Band 2-conformations are tilted a t angles greater than 19O with respect to the helix axis. The guanine and cytosine bases have different inclinations, and the tilt axes are not parallel. Therefore, the bases for all the (G + C) polymer conformations studied are buckled and propeller twisted.

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