@article{780516f49d7c49978fa65bf62023e1cb,
title = "The spatial configuration of ordered polynucleotide chains. II. The poly(rA) helix",
abstract = "Approximate details of the spatial configuration of the ordered single-stranded poly(rA) molecule in dilute solution have been obtained in a combined theoretical analysis of base stacking and chain flexibility. Only those regularly repeating structures which fulfill the criterion of conformational flexibility (based upon all available experimental and theoretical evidence of preferred bond rotations) and which also exhibit the right-handed base stacking pattern observed in nmr investigations of poly(rA) are deemed suitable single-stranded helices. In addition, the helical geometry of the stacked structures is required to be consistent with the experimentally observed dimensions of both completely ordered and partially ordered poly(rA) chains. Only a single category of poly(rA) helices (very similar in all conformational details to the individual chains of the poly(rA) double-stranded X-ray structure) is thus obtained. Other conformationally feasible polynucleotide helices characterized simply by a parallel and overlapping base stacking arrangement are also discussed.",
author = "Olson, {Wilma K.}",
note = "Funding Information: adenine bases1{"}3'5'6 and the 3.5 approximately the experimentally ly ordered poly(rA) chains. It is important to recognize that the approximate description of the single-stranded poly(rA) molecule outlined above in no way requires that the set of internal rotations along the chain conform exactly to the values observed in the poly(rA) double helix. It is interesting to observe, nevertheless, that the ordered chain residues which best approximate the observed dependence of the unperturbed dimensions of the partially stacked poly(rA) molecule with decreasing temperature are units described by helical parameters very similar to those of the poly(rA) double helix. The double helix chains o are characterized by a step height z = 3.8 A, a radius (phosphorus atoms) r = o 5.95 A, and a repeating angle e = 45°.26 The mean helical parameters of the two theoretical chains (3 and 4 from Table IV) which best approximate the oo partially stacked dimensions are z = 4.1 A, r = 5.51 A, and e = 40.9°. The calculated unperturbed dimensions of poly(rA) molecules containing more loosely wound helical units similar to the RNA X-ray structures (where r - 8 to 10 o A and 9 - 30-36°)15 are not comparable in magnitude to the observed experimental values. ACKNOWLEDGMENTS The author is grateful to the Research Corporation, the donors of the Petroleum Research Fund administered by the American Chemical Society-, and to the National Institutes of Health (U.S.P.H.S. Grant GM 20861) for laboratory support, to the Center for Computer and Information Services of Rutgers University for com'puter time, and to Rama Dasika and Carol Oken for technical assistance. W.K.O. is also a Public Health Service Research Career Development Awardee (GM 00155). *Part I of this series is reference 15.",
year = "1975",
month = nov,
doi = "10.1093/nar/2.11.2055",
language = "English (US)",
volume = "2",
pages = "2055--2068",
journal = "Nucleic acids research",
issn = "0305-1048",
publisher = "Oxford University Press",
number = "11",
}