The rep region of pR plasmid regulates the expression of SOS system

Area of Science:

• Molecular Biology
• Bacteriology
• Genetics

Background:

• The muc genes in plasmids are crucial for bacterial adaptation, mediating increased spontaneous mutagenesis and resistance to environmental stressors like UV radiation and chemicals.
• These muc genes are under the negative control of the lexA regulatory protein, a key component in bacterial DNA damage response pathways.

Purpose of the Study:

• To identify and characterize the regulatory function within the pR plasmid's rep region that influences muc gene expression.
• To elucidate the mechanism by which this pR plasmid function interacts with the bacterial lexA system.

Main Methods:

• Construction of an artificial hybrid between phage lambda and the pR plasmid.
• Utilizing a lacZ gene fusion to monitor muc gene promoter activity.
• Employing deletion mapping to precisely locate the functional gene within the pR plasmid's rep region.
• Assessing the impact of the pR plasmid hybrid on lambda phage virulence in E. coli.

Main Results:

• The pR plasmid's rep region encodes a function that enhances the expression of muc genes, indicating antagonism towards lexA.
• Deletion mapping identified the antagonist of lexA (bat) gene within the pR plasmid's rep region.
• The bat gene product was also found to antagonize the lambda cI repressor, leading to virulent phage behavior on homoimmune lysogens.
• Genetic and functional analysis revealed the bat region operates as an operon, with its expression negatively regulated by a repressor gene.

Conclusions:

• The pR plasmid harbors a novel gene, bat, which antagonizes the lexA repressor, thereby regulating muc gene expression and associated phenotypes.
• The bat gene product's ability to antagonize both lexA and lambda cI repressors offers a unique tool for studying gene regulation and bacterial defense mechanisms.