cmp, a cis-acting plasmid locus that increases interaction between replication origin and initiator protein.

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• The pT181 plasmid from Staphylococcus aureus is a multicopy plasmid crucial for bacterial survival.
• Replication of pT181 is regulated by the RepC initiator protein, which acts as a rate-limiting factor.

Purpose of the Study:

• To investigate the role of a specific plasmid region in competition with other plasmids.
• To understand the mechanism by which this region affects plasmid replication and coexistence.

Main Methods:

• Plasmid deletion analysis of the pT181 4.4-kilobase sequence.
• Competition assays with coexisting incompatible plasmids.
• Assessment of copy number and plasmid stability in homoplasmid states.

Main Results:

• Deletions in a 500-base-pair region, termed cmp (competition), impaired the plasmid's ability to compete.
• The cmp region appears to modulate the interaction between RepC and the plasmid origin of replication.
• These deletions did not affect plasmid copy number or stability in the absence of competing plasmids.
• The competition defect was orientation-independent and could not be complemented in trans.

Conclusions:

• The cmp region is essential for efficient competition between pT181 plasmids.
• This region plays a regulatory role in plasmid replication initiation, specifically impacting RepC-origin interactions.
• The findings provide insights into plasmid incompatibility and coexistence mechanisms in Staphylococcus aureus.