Interacting interfaces of the P4 antirepressor E and the P2 immunity repressor C

Area of Science:

• Molecular Biology
• Microbiology
• Genetics

Background:

• Antirepressors activate gene expression by interacting with transcriptional repressors.
• Satellite phage P4 requires helper phage functions for lytic growth.
• P4 phage utilizes its E protein to derepress the unrelated P2 prophage.

Purpose of the Study:

• Investigate the mechanism of P4 E protein-mediated derepression of P2 prophage.
• Characterize the P2 mutant 'sos' and its insensitivity to P4 E protein.
• Elucidate the molecular interactions between P4 E protein and P2 repressor C.

Main Methods:

• Two-plasmid reporter system to assess transcriptional switching.
• Yeast two-hybrid system to analyze protein-protein interactions.
• Site-directed mutagenesis to identify critical domains and mutations.

Main Results:

• The P2 'sos' mutation is a point mutation in the C repressor gene, blocking P4 E protein's ability to induce P2 lytic development.
• The 'sos' mutation disrupts the interaction between P4 E protein and P2 C repressor.
• P2 C repressor dimerization is C-terminal; 'sos' mutation does not affect dimerization but blocks E interaction.
• Compensatory P4 E mutants interacting with 'sos' C repressor cannot induce P2 lysis.

Conclusions:

• The P4 E protein's antirepressor function is mediated by specific interaction with the P2 C repressor.
• The 'sos' mutation in P2 C repressor highlights the critical interface for antirepressor binding.
• Understanding these interactions provides insights into phage-host regulatory mechanisms and antirepressor function.