Structure of Poly (U).poly (A).poly (U) |
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Authors: | Chandrasekaran R Giacometti A Arnott S |
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Institution: | Whistler Center for Carbohydrate Research, Purdue University, West Lafayette, IN 47907, USA. chandra@purdue.edu |
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Abstract: | The molecular structure of poly (U).poly (A).poly (U) has been determined and refined using the continuous x-ray intensity data on layer lines in the diffraction pattern obtained from an oriented fiber of the RNA. The final R-value for the preferred structure is 0.24, far lower than that for the plausible alternatives. The polymer forms an 11-fold right-handed triple-helix of pitch 33.5A and each base triplet is stabilized by Crick-Watson-Hoogsteen hydrogen bonds. The ribose rings in the three strands have C3'-endo, C2'-endo and C2'-endo conformations, respectively. The helix derives additional stability through systematic interchain hydrogen bonds involving ribose hydroxyls and uracil bases. The relatively grooveless cylindrical shape of the triple-helix is consistent with the lack of lateral organization. |
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