Diagrammatic approaches to RNA structures with trinucleotide repeats

Area of Science:

• Molecular Biology
• Genetics
• Biophysics

Background:

• Trinucleotide repeat expansion disorders are linked to overexpanded (CNG) repeats in the genome.
• RNA transcripts with over 60-100 (CNG) tandem units are implicated in disease pathogenesis.

Purpose of the Study:

• To develop a theoretical framework for studying the structural diversity of (CNG)n RNA sequences.
• To analyze the ensemble of possible RNA conformations, including duplexes, hairpins, junctions, and quadruplexes.

Main Methods:

• A diagrammatic theory was developed to represent RNA structural elements as graphs.
• A renormalization procedure was employed to re-sum graphs and derive a closed-form expression for the ensemble partition function.
• Analytical equations were solved numerically to estimate secondary structural contents.

Main Results:

• The theory captures an infinite set of conformations for (CNG)n sequences.
• Structural ensembles for sequences with n ~60 repeats are highly diverse.
• Diversity is sensitive to noncanonical base pairing and quadruplex stability.

Conclusions:

• The diagrammatic theory provides a comprehensive method to analyze RNA structural diversity in trinucleotide repeat disorders.
• Perturbations in the stability of structural motifs can significantly alter RNA secondary structures.
• Understanding these structural dynamics is crucial for deciphering disease mechanisms.