Nucleic Acids Research, Vol 25, Issue 20 4018-4027, Copyright © 1997 by Oxford University Press
P Burgstaller, T Hermann, C Huber, E Westhof and M Famulok
We have recently shown that isoalloxazine derivatives are able to
photocleave RNA specifically at G.U base pairs embedded within a helical
stack. The reaction involves the selective molecular recognition of G.U
base pairs by the isoalloxazine ring and the removal of one nucleoside
downstream of the uracil residue. Divalent metal ions are absolutely
required for cleavage. Here we extend our studies to complex natural RNA
molecules with known secondary and tertiary structures, such as tRNAs and a
group I intron (td). G.U pairs were cleaved in accordance with the
phylogenetically and experimentally derived secondary and tertiary
structures. Tandem G.U pairs or certain G.U pairs located at a helix
extremity were not affected. These new cleavage data, together with the RNA
crystal structure, allowed us to perform molecular dynamics simulations to
provide a structural basis for the observed specificity. We present a
stable structural model for the ternary complex of the G. U-containing
helical stack, the isoalloxazine molecule and a metal ion. This model
provides significant new insight into several aspects of the cleavage
phenomenon, mechanism and specificity for G. U pairs. Our study shows that
in large natural RNAs a secondary structure motif made of an unusual base
pair can be recognized and cleaved with high specificity by a low molecular
weight molecule. This photocleavage reaction thus opens up the possibility
of probing the accessibility of G.U base pairs, which are endowed with
specific structural and functional roles in numerous structured and
catalytic RNAs and interactions of RNA with proteins, in folded RNAs.
ARTICLES
Isoalloxazine derivatives promote photocleavage of natural RNAs at G.U base pairs embedded within helices
Institut fur Biochemie der LMU Munchen-Genzentrum, Wurmtalstrasse 221, 81375 Munchen, Germany.
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