Single-Stranded Condensation Stochastically Blocks G-Quadruplex Assembly in Human Telomeric RNA

Area of Science:

• Molecular Biology
• Biophysics
• Genetics

Background:

• TERRA (Telomeric Repeat-containing RNA) is transcribed from human subtelomeric regions.
• TERRA has a propensity to form parallel G-quadruplex structures due to its GGGUUA repeat sequence.
• Potential roles of TERRA include regulation of heterochromatin stability, replication, and telomerase inhibition.

Purpose of the Study:

• To investigate the folding behavior of TERRA molecules using single-molecule force spectroscopy.
• To determine the influence of RNA self-association and condensation on G-quadruplex formation.
• To compare the folding properties of TERRA with analogous DNA molecules.

Main Methods:

• Single-molecule force spectroscopy utilizing optical tweezers.
• Stretching of RNA constructs with varying numbers of hexanucleotide repeats (4-8).
• Employing non-G-rich overhangs of random sequence to flank the RNA constructs.

Main Results:

• Random RNA self-association and condensation limit the potential for G-quadruplex formation.
• Condensed RNA stochastically blocks G-quadruplex folding pathways with approximately 20% probability.
• This blocking behavior was not observed in analogous DNA molecules.

Conclusions:

• The inherent capacity of RNA to self-associate and condense into entropically favorable structures impedes G-quadruplex formation.
• TERRA's folding pathways are significantly influenced by these stochastic condensation events.
• RNA and DNA exhibit distinct behaviors regarding G-quadruplex formation due to differences in self-association properties.