Structure of an unmodified tRNA molecule.

Area of Science:

• Structural Biology
• Biochemistry
• Molecular Biophysics

Background:

• Transfer RNA (tRNA) plays a crucial role in protein synthesis.
• Understanding tRNA structure is essential for deciphering its biological functions.
• Yeast tRNA(Phe) is a well-studied model system for tRNA research.

Purpose of the Study:

• To investigate the structure of yeast tRNA(Phe) synthesized via T7 RNA polymerase using NMR spectroscopy.
• To determine the influence of magnesium ion (Mg2+) concentration on tRNA(Phe) folding and structure.
• To analyze the structural basis for the aminoacylation activity of the synthesized tRNA(Phe) transcript.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy, specifically imino proton (1H) spectra.
• Analysis of chemical shifts and Nuclear Overhauser Effect (NOE) patterns.
• Assessment of aminoacylation kinetics.

Main Results:

• NMR assignments were obtained for imino resonances, including those involved in tertiary interactions.
• High Mg2+ concentrations facilitated normal folding, yielding spectral features similar to native tRNA(Phe).
• Low Mg2+ conditions (<0.2 [tRNA]:[Mg2+] ratio) led to non-native structures, characterized by altered chemical shifts, NOE patterns, and a second GU base pair.
• A G20U mutant exhibited a structure nearly identical to the wild-type, suggesting conformational similarity despite altered aminoacylation activity.

Conclusions:

• The synthesized yeast tRNA(Phe) transcript folds into a native-like structure at high Mg2+ concentrations, confirmed by NMR and aminoacylation kinetics.
• Magnesium ions are critical for maintaining the native tertiary structure of tRNA(Phe).
• The observed structural rearrangement in low Mg2+ conditions highlights the ion-dependent nature of tRNA folding.
• The G20U mutation's minimal conformational impact suggests its reduced aminoacylation activity is not due to major structural deviations.