Nuclease recognition of an alternating structure in a d(AT)14 plasmid insert

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• Poly(dA-dT) sequences are known for their unique structural properties within DNA.
• Understanding the reactivity of these sequences is crucial for comprehending DNA structure-function relationships.

Purpose of the Study:

• To investigate the nuclease reactivity and specificity of cloned poly(dA-dT) tracts.
• To elucidate the structural characteristics of alternating AT sequences in DNA.

Main Methods:

• Digestion of a 256 base pair restriction fragment containing d(AT)14A with various nucleases (DNAse I, Mung Bean nuclease, S1 nuclease, DNAse II).
• Treatment with copper (1,10-phenanthroline)2.
• Analysis of DNA cleavage patterns under varying DNA supercoiling conditions.

Main Results:

• A dinucleotide repeat structure was identified within the alternating AT sequence.
• The AT insert's reactivity was largely unaffected by DNA winding or unwinding.
• Preferred cleavage sites suggest structural alterations distinct from A, B, or Z-DNA forms.

Conclusions:

• Poly(dA-dT) tracts possess a unique structural motif characterized by dinucleotide repeats.
• This structural alteration influences DNA helix conformation without affecting flanking sequences.
• The findings provide insights into non-canonical DNA structures and their enzymatic recognition.