Nucleic Acids Research, 1989, Vol. 17, No. 22 9075-9086
© 1989
CHEMISTRY |
Mercury-Induced transitions between right-handed and putative left-handed forms of poly[d(A-T)·d(A-T)] and poly[d(G-C)·d[(G-C)]
Department of Food Science and Technology University of California Davis, CA 95616, USA
*To whom correspondence should be addressed
Received August 18, 1989. Revised October 12, 1989. Accepted October 12, 1989.
Poly[d(A-T)·d(A-T)] and poly[d(G-C)·d(G-C)], each dissolved in 0.1 M NaClO4 5 mM cacodylic acid buffer, pH 6.8, experience inversion of their circular dichroism (CD) spectrum subsequent to the addition of Hg(ClO4)2. Let r = [Hg(ClO4)2]added/[DNA-P]The spectrum of the right-handed form of poly [d(A-T)·d(A-T)] turns into that of a seemingly left-handed structure at r 
0.05 while a similar transition is noted with poly [d(G-C)·(G-C)] at r 0.12. The spectral changes are highly cooperative in the long-wavelength region above 250 nm. At r = 1.0, the spectra of the two polymers are more or less mirror images of their CD at r = 0. While most CD bands experience red-shifts upon the addition of Hg(ClO4)2 there are some that are blue-shifted. The CD changes are totally reversible when Hg(II) is removed from the nucleic acids by the addition of a strong complexing agent such as NaCN. This demonstrates that mercury keeps all base pairs in register.