Proteus mirabilis chromosome mobilization by plasmid D: a physical characterization

Area of Science:

• Bacteriology
• Molecular Biology
• Genetics

Background:

• Plasmid D, a hybrid of P-lac and R1 drd19, exhibits chromosome mobilization in Proteus mirabilis.
• Parental plasmids P-lac and R1 drd19 do not individually or combined mobilize the chromosome.

Purpose of the Study:

• To physically characterize plasmid D and elucidate its acquired chromosome mobilizing ability.
• To understand the genetic basis of plasmid D's unique function.

Main Methods:

• Restriction pattern analysis of plasmids D, P-lac, and R1 drd19.
• In vitro insertion of plasmid D fragments into IncP-1 plasmid RP4.
• Analysis of chromosome mobilization and host characteristics.

Main Results:

• Plasmid D comprises P-lac and the r-determinant (r-det) of R1 drd19, with IS1 involvement suggested in its formation.
• RP4::HindIII beta plasmids, containing a specific fragment in opposite orientations, mediated chromosome mobilization.
• One orientation (pMC17) mimicked plasmid D's single-origin mobilization, while the other (pMC1) mobilized from two origins, deviating from typical inversion effects.

Conclusions:

• The r-determinant, integrated into P-lac via IS1, confers chromosome mobilizing ability.
• The orientation and specific DNA fragment are critical for the origin and mechanism of chromosome mobilization.
• Plasmid D's unique mobilization mechanism provides insights into plasmid-mediated genetic exchange.