Cover: NMR structures of two loops in a high affinity RNA aptamer against mammalian initiation factor 4A (eIF4A) are shown. G, A, U, and C residues are colored in blue, red, green, and yellow, respectively. The AUCGCA loop (left) is stabilized by a U-turn motif and contains a non-canonical A:A base pair (with a single hydrogen bond mismatch: Hoogsteen/Sugar-edge). On the other hand, the ACAUAGA loop (right) is stabilized by an AUA tri-nucleotide loop motif and contains another type of A:A base pair (single hydrogen bond mismatch: Watson-Crick/Watson-Crick). We propose that the conformations of the double loops are important for the aptamer's global recognition of eIF4A. For further details see the paper by Sakamoto et al. in this issue: Nucleic Acids Res. (2005), 33, 745-754.
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