Photo-Cross-Linking between ^Br U and Pyrene Residues in an RNA/DNA Hybrid

Area of Science:

• Biochemistry
• Molecular Biology
• Photochemistry

Background:

• Bromouracil (BrU) is a modified nucleobase used in photochemical studies.
• Nucleic acid duplexes exist in different forms, such as A-form and B-form, with distinct structural properties.
• Understanding molecular interactions within nucleic acids is crucial for various biological processes.

Purpose of the Study:

• To investigate the photoreaction of bromouracil (BrU) in pyrene-labeled DNA duplexes, RNA duplexes, and DNA/RNA hybrids.
• To determine how changes in duplex conformation (A-form vs. B-form) affect BrU photoreactivity.
• To explore the utility of BrU reactivity in analyzing the contact between small molecules and nucleic acids.

Main Methods:

• Incorporation of bromouracil (BrU) into DNA, RNA, and hybrid duplexes.
• Labeling with pyrene to probe molecular interactions.
• Photochemical reactions and analysis of cross-linked products.
• Comparison of photoreactivity in A-form and B-form nucleic acid structures.

Main Results:

• Photoreactivity of BrU shifted from hydrogen abstraction to cross-linking upon changing duplex conformation from B-form to A-form.
• The highest yield of cross-linked products was observed in A-form structures with BrU in the RNA strand and pyrene at the 5' end of DNA.
• These findings suggest distinct pyrene contact modes in A-form versus B-form duplexes.

Conclusions:

• Duplex conformation significantly influences bromouracil photoreactivity and cross-linking.
• The specific placement of BrU and pyrene affects interaction dynamics in A-form structures.
• Bromouracil's reactivity offers a novel approach to study weak interactions between small molecules and nucleic acids.