A.T and C.C+ base pairs can form simultaneously in a novel multistranded DNA complex

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• Previous research indicated that adenine-thymine (A.T) base pairs can form to the exclusion of protonated cytosine-cytosine (C.C+) base pairs in specific synthetic DNA oligomers.
• Understanding DNA base pairing preferences is crucial for comprehending DNA structure, stability, and function.

Purpose of the Study:

• To investigate the base pairing behavior of two additional classes of DNA oligomers concerning the formation of A.T and C.C+ base pairs.
• To determine if C.C+ base pairs form preferentially over A.T base pairs in novel DNA sequences.

Main Methods:

• Circular dichroism (CD) spectroscopy was employed to monitor changes in DNA structure.
• High-performance liquid chromatography (HPLC) and centrifugation were used to analyze DNA oligomer behavior.
• Studies were conducted across varying pH and sodium ion (Na+) concentrations to induce and observe base pairing.

Main Results:

• DNA oligomers d(CCAAT)3-6 and d(AATCC)4,5 showed spectral evidence of C.C+ base pair formation as pH decreased, with no detectable A.T base pairing.
• As much as 40% C.C+ base pairs were stable in these sequences without adjacent or alternative A.T pairing.
• The oligomer d(C4A4T4C4) confirmed previous findings, demonstrating the ability to form both A.T and C.C+ base pairs under specific pH and temperature conditions.

Conclusions:

• Certain DNA sequences exhibit a strong preference for forming C.C+ base pairs, excluding A.T base pairing.
• The stability of C.C+ base pairs in these sequences suggests specific structural constraints or favorable interactions.
• These findings contribute to the understanding of DNA sequence-dependent base pairing and structural polymorphism.