Structure of Poly (U).poly (A).poly (U).

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Polyribonucleotides play crucial roles in biological processes.
• Understanding the higher-order structure of RNA is essential for elucidating its function.
• Poly(U).poly(A).poly(U) is a synthetic RNA complex with potential implications for RNA structure research.

Purpose of the Study:

• To determine and refine the molecular structure of the poly(U).poly(A).poly(U) triple helix.
• To elucidate the hydrogen bonding patterns and conformational details of the RNA polymer.
• To correlate the determined structure with observed physical properties.

Main Methods:

• X-ray diffraction analysis of oriented RNA fibers.
• Collection and analysis of continuous x-ray intensity data on layer lines.
• Structure refinement using established crystallographic methods.

Main Results:

• The molecular structure was refined to a final R-value of 0.24.
• A preferred structure of an 11-fold right-handed triple-helix with a pitch of 33.5A was identified.
• Base triplets are stabilized by Crick-Watson-Hoogsteen hydrogen bonds.
• Ribose rings exhibit distinct C3'-endo and C2'-endo conformations across the three strands.
• Interchain hydrogen bonds involving ribose hydroxyls and uracil bases contribute to helix stability.
• The triple-helix possesses a cylindrical shape with minimal grooves, correlating with a lack of lateral organization.

Conclusions:

• The study successfully elucidated the detailed molecular structure of poly(U).poly(A).poly(U).
• The identified triple-helical structure and hydrogen bonding network provide insights into RNA structural motifs.
• The findings contribute to the broader understanding of RNA folding and intermolecular interactions.