Left-handed DNA in vivo

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• DNA can adopt non-canonical helical structures beyond the standard B-form.
• Left-handed DNA helices, such as Z-DNA, and cruciform structures can form under specific conditions.
• The biological relevance and cellular responses to these alternative DNA structures are not fully understood.

Purpose of the Study:

• To investigate the biological activity of left-handed DNA helices in Escherichia coli.
• To determine if alternative DNA structures can elicit specific cellular responses.
• To examine the interaction of left-handed DNA with DNA methylase enzymes in vivo and in vitro.

Main Methods:

• Utilized plasmids with inserts designed to form left-handed helices or cruciforms.
• Employed a temperature-sensitive Eco RI methylase (MEco RI) for in vivo and in vitro methylation assays.
• Assessed inhibition of methylation, supercoil-induced structural changes, and plasmid incompatibilities.
• Confirmed structural properties through in vitro studies of supercoil-induced helix changes.

Main Results:

• Inhibition of MEco RI methylation was observed in vivo for inserts forming stable, long left-handed helices.
• In vitro methylation experiments corroborated the in vivo findings.
• Supercoil-induced structural transitions in vitro confirmed the role of left-handed helices.
• The presence of left-handed DNA inserts in vivo led to specific deletions and plasmid incompatibilities.

Conclusions:

• Left-handed DNA structures, including Z-DNA, are biologically active in Escherichia coli.
• These alternative DNA conformations can interfere with enzymatic processes like DNA methylation.
• Left-handed DNA can induce genetic instability, manifesting as deletions and plasmid incompatibility.
• The study provides evidence for the functional significance of non-canonical DNA structures within a cellular context.