Secondary structure of the r(CUUCGG) tetraloop

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Oligonucleotides can adopt different conformations.
• An RNA dodecamer r(GGACUUCGGUCC) exhibits distinct structures under different experimental conditions.

Purpose of the Study:

• To resolve the discrepancy between hairpin and double helical conformations observed for an RNA dodecamer.
• To elucidate the factors influencing the secondary structure of this oligonucleotide.

Main Methods:

• Time-resolved fluorescence depolarization
• 19F NMR spectroscopy
• Stepwise alteration of solution conditions (salt concentration, concentration)

Main Results:

• The RNA dodecamer maintains a hairpin conformation in solution even under crystallization conditions.
• High salt concentrations and tethered species (dimers) promote the formation of double helical structures.
• Crystal contacts, solvent changes, and high concentrations are crucial for the double helix to become the predominant species.

Conclusions:

• The observed conformational differences are attributed to variations in solution conditions and intermolecular interactions.
• High concentrations and specific environmental factors, such as crystal contacts, drive the formation of the double helical structure.
• Understanding these factors is critical for predicting and controlling oligonucleotide secondary structures.