Triplex DNA in plasmids and chromosomes

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Circular plasmids with pyrimidine-purine tracts are capable of forming DNA triplex structures.
• These triplexes can form through intermolecular or intramolecular associations.

Purpose of the Study:

• To investigate the formation and characteristics of DNA triplexes in circular plasmids.
• To determine the conditions favoring inter- and intramolecular triplex formation.
• To assess the presence of triplex structures in different cellular environments.

Main Methods:

• Plasmid manipulation and addition of synthetic DNA strands (poly(dTC)).
• Agarose-gel electrophoresis to analyze complex formation.
• Electron microscopy to visualize triplex structures.
• Monoclonal antibody (Jel318) for triplex detection and mobility shift assays.
• Immunoblotting to detect triplexes in cellular extracts.

Main Results:

• Addition of poly(dTC) induced intermolecular triplex formation in plasmid pTC45, visualized as rosette structures.
• Intramolecular triplex formation was observed at low pH (pH 5) in plasmids pTC45 and pT463-I.
• Intermolecular triplexes were stable at pH 8, while intramolecular triplexes required acidic conditions.
• The monoclonal antibody Jel318 specifically recognized and retarded the mobility of triplex-containing complexes.
• Triplex structures were detected in eukaryotic cell extracts but not in Escherichia coli extracts.

Conclusions:

• DNA triplex formation is a demonstrable phenomenon in circular plasmids under specific conditions.
• The stability and formation of triplexes are pH-dependent.
• Triplex structures are associated with eukaryotic cellular machinery and may play a role in eukaryotic chromosome organization.