A copy-number mutant of plasmid pSC101

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• Plasmid copy number is a critical factor in genetic engineering and biotechnology.
• The RepA protein regulates the replication of plasmid pSC101.
• Understanding the mechanisms controlling plasmid copy number is essential for optimizing plasmid-based systems.

Purpose of the Study:

• To investigate the genetic basis of elevated plasmid pSC101 copy number.
• To identify specific mutations affecting RepA protein function and their impact on plasmid replication.

Main Methods:

• Isolation of copy-number mutants using UV mutagenesis and ampicillin resistance selection.
• Mapping of mutations to the RepA initiation protein gene.
• Quantification of RepA mRNA and protein expression levels.
• Measurement of RepA protein binding affinity to origin DNA sequences.

Main Results:

• Three independent mutations conferring higher plasmid copy number mapped to codon 93 of the RepA gene.
• Mutated plasmids were maintained at 4-5 times higher levels than wild-type.
• RepA mRNA and protein levels were 1.7 times higher in mutants.
• Mutated RepA protein showed a 3.4-fold increased affinity for origin DNA sequences.

Conclusions:

• Elevated plasmid pSC101 copy number is caused by mutations in the RepA protein.
• The increased copy number results from a combination of higher RepA protein concentration and enhanced binding affinity to origin sequences.
• These findings provide insights into plasmid replication control and offer potential strategies for manipulating plasmid copy number.