Structural polymorphism of the four-repeat Oxytricha nova telomeric DNA sequences.

Area of Science:

• Biochemistry
• Molecular Biology
• Genetics

Background:

• G-quadruplexes are polymorphic four-stranded nucleic acid structures.
• Previous work characterized the polymorphism of Oxytricha nova telomeric sequences.

Purpose of the Study:

• To evaluate the effects of G-tract and loop lengths on G-quadruplex polymorphism.
• To understand how sequence variations influence G-quadruplex formation in the presence of cations.

Main Methods:

• Circular dichroism (CD) spectroscopy.
• Gel electrophoresis.
• Analysis of synthetic DNA oligonucleotides.

Main Results:

• The number of consecutive G residues (G-tract length) had the largest impact on G-quadruplex polymorphism.
• Shortening loop lengths from four to three residues caused only minor alterations.
• Shortening G-tracts from four to three guanine residues resulted in anti-parallel G-quadruplex CD spectra.
• Adenine in loop sequences reduced G-quadruplex formation with Na+ compared to thymine.

Conclusions:

• G-quadruplex folding is sensitive to G-tract length, with shorter tracts favoring anti-parallel structures.
• Loop length has a less pronounced effect on G-quadruplex polymorphism.
• Sequence composition, particularly adenine vs. thymine in loops, influences cation-mediated G-quadruplex formation, aiding predictive models.