1i9k

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spinqualitylabelsall models PDB ID 1i9k Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image
Ligands:	,
Resources:	FirstGlance, OCA, PDBsum, RCSB
Coordinates:	save as pdb, mmCIF, xml

THE RNA I-MOTIF

Overview

Oligodeoxynucleotides with stretches of cytidine residues associate into a four-stranded structure, the i-motif, in which two head-to-tail, intercalated, parallel-stranded duplexes are held together by hemiprotonated C.C+ pairs. We have investigated the possibility of forming an i-motif structure with C-rich ribonucleic acids. The four C-rich RNAs studied, r(UC5), r(C5), r(C5U) and r(UC3), associate into multiple intercalated structures at acidic pH. r(UC5) forms two i-motif structures that differ by their intercalation topologies. We report on a structural study of the main form and we analyze the small conformational differences found by comparison with the DNA i-motif. The stacking topology of the main structure avoids one of the six 2'-OH/2'-OH repulsive contacts expected in a fully intercalated structure. The C3'-endo pucker of the RNA sugars and the orientation of the intercalated C.C+ pairs result in a modest widening of the narrow grooves at the steps where the hydroxyl groups are in close contact. The free energy of the RNA i-motif, on average -4 kJ mol(-1) per C.C+ pair, is half of the value found in DNA i-motif structures.

About this Structure

1I9K is a Protein complex structure of sequences from [1]. Full crystallographic information is available from OCA.

Reference

The RNA i-motif., Snoussi K, Nonin-Lecomte S, Leroy JL, J Mol Biol. 2001 May 25;309(1):139-53. PMID:11491284

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