The PX Motif of DNA Binds Specifically to Escherichia coli DNA Polymerase I

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• The PX DNA motif is a unique four-stranded DNA structure with distinct topological properties, including reduced twist and writhe compared to conventional DNA.
• This motif can relax supercoiled plasmid DNA when specific homologous sequences (PX homology) are present, indicating potential biological relevance.
• The existence of cellular proteins interacting with this unusual DNA structure is of significant interest for understanding its function.

Purpose of the Study:

• To investigate whether proteins within Escherichia coli (E. coli) interact with the PX DNA motif.
• To identify and characterize any cellular components that bind to the PX DNA structure.

Main Methods:

• Gel mobility shift assays were employed to detect binding of cellular components to the PX DNA motif.
• Fractionation of E. coli extracts was performed to isolate the binding activity.
• Molecular dynamics and symmetry considerations were used to model the interaction between DNA polymerase I and the PX DNA motif.

Main Results:

• Gel mobility studies indicated that a cellular component in E. coli extracts binds to the PX DNA motif.
• Purification of the binding activity identified DNA polymerase I (Pol I) as the interacting protein.
• Despite binding, PX-DNA did not function as a substrate for Pol I-mediated strand extension.

Conclusions:

• Escherichia coli DNA polymerase I (Pol I) binds to the four-stranded PX DNA motif.
• The functional significance of this interaction remains unclear, as Pol I does not appear to process the PX-DNA structure.
• This binding may represent a novel, yet undiscovered, activity of Pol I or be a coincidental interaction.