Base-base interactions in nucleic acids containing A-T base pairs. Structure of poly[d(A-T)]

Area of Science:

• Molecular Biology
• Biophysics
• Structural Chemistry

Background:

• Watson-Crick base pairing is the canonical model for DNA duplex formation.
• Alternative base pairing modes, such as Hoogsteen pairing, are less understood in DNA structures.
• Conformational flexibility in DNA may allow for non-canonical base pairing.

Purpose of the Study:

• To investigate the feasibility of Hoogsteen type base pairing in A-T containing DNA sequences.
• To identify and analyze viable structural models for polynucleotide duplexes utilizing Hoogsteen base pairing.
• To compare the energetic stability of Hoogsteen versus Watson-Crick base pairing in specific DNA contexts.

Main Methods:

• Utilized conformational calculations to explore DNA backbone torsion angles and sugar pucker.
• Performed energy calculations on A-T containing doublet sequences in the D-form.
• Developed and analyzed three distinct structural models for poly[d(A-T)] duplexes.

Main Results:

• Demonstrated that specific combinations of backbone torsion angles and sugar pucker enable Hoogsteen base pairing in A-T sequences.
• Identified three viable structural models for A-T containing polynucleotide duplexes with Hoogsteen base pairing.
• Provided energetic data supporting the possibility of Hoogsteen pairing in certain DNA conformations.

Conclusions:

• Hoogsteen base pairing is a viable alternative to Watson-Crick pairing in A-T containing DNA duplexes under specific conformational conditions.
• The findings challenge the notion that Watson-Crick pairing is exclusively mandatory for DNA duplex formation.
• The identified models offer new insights into DNA structural diversity and alternative base-pairing mechanisms.