An inverted repeat sequence of the IncFI plasmid ColV2-K94 increases multimerization-mediated plasmid instability

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• The IncFI plasmid ColV2-K94 harbors a Rep1 replicon, Tn903 transposon, and an X1 inverted repeat structure.
• Plasmid stability is crucial for maintaining genetic information in bacterial populations.

Purpose of the Study:

• To investigate the properties and effects of the X1 inverted repeat structure on plasmid maintenance.
• To determine the mechanism underlying the destabilizing effect of the X1 sequence.

Main Methods:

• Physical mapping of the ColV2-K94 plasmid region.
• Cloning restriction fragments into pBR325 and pBR322 vectors.
• Assessing plasmid stability and copy number in RecA, RecB, and RecC deficient host strains.

Main Results:

• The 1.2 kb repeated sequence of X1, but not IS903, destabilized pBR325 and pBR322 plasmid maintenance.
• Plasmid derivatives containing X1 showed increased multimeric DNA forms, reduced copy number, and instability.
• The destabilizing effect of X1 was dependent on the host RecA function, but not RecB or RecC.

Conclusions:

• The X1 inverted repeat sequence acts as a recombination hot-spot, promoting generalized recombination.
• Enhanced recombination at the X1 site leads to plasmid multimerization and instability when present in cis.
• RecA-mediated recombination is responsible for the instability induced by the X1 structure in plasmids.