期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1981
卷号：78
期号：11
页码：6808-6811
DOI：10.1073/pnas.78.11.6808
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：We report transient electric dichroism studies of short double-helical DNA and poly[d(G-C)] fragments in alcohol/water mixtures. The limiting reduced dichroism and the rotational correlation time changed abruptly in the alcohol concentration range expected for the DNA B-to-A and poly[d(G-C)] B-to-Z transitions. The Z form of poly[d(G-C)] was also induced by mitomycin C crosslinking in aqueous solution. The rotational correlation times observed for A- and Z-DNA were approximately consistent with dimensions determined by crystallographic and fiber diffraction analysis: the estimated rise per base pair was 2.8 A for A-DNA and 3.7 A for Z-DNA in solution. In addition, the observed limiting reduced dichroism values for A- and Z-DNA were close to the theoretical limit of -1.5, requiring a structure in which the base transition moments are effectively perpendicular to the double-helix axis. This is the result expected for any DNA double helix having dyad symmetry in which the base pairs are flat and the base transition moments lie predominantly in the short axis of the base pair and therefore close to a helix dyad axis. Only B-DNA deviates from this rule, strongly reinforcing our earlier conclusion that the base pairs in B-DNA are not flat but are propeller twisted, either statically or as a dynamic average.
