A DNA recognition-mimicry switch governs induction in arbitrium phages.

Area of Science:

• Microbiology
• Molecular Biology
• Virology

Background:

• Temperate phages regulate lysis-lysogeny based on environmental cues.
• SPbeta-like phages utilize arbitrium signaling and DNA damage for lytic induction.
• The precise mechanism of repressor inactivation by the SOS response was unclear.

Purpose of the Study:

• To elucidate the mechanism of SPbeta-like phage repressor function and inactivation.
• To understand how the SOS response controls phage induction.
• To investigate the role of arbitrium signaling in conjunction with repressor inactivation.

Main Methods:

• Investigated the DNA-binding mechanism of the SPbeta-like phage repressor, SroF.
• Characterized the interaction between the antirepressor, Sar, and SroF.
• Analyzed the impact of arbitrium levels on phage induction efficiency.

Main Results:

• SroF, the phage repressor, binds DNA using an integrase-like fold for stable repression.
• Host SOS response induces antirepressor Sar, which inactivates SroF by mimicking DNA.
• Phage induction requires both repressor inactivation and low arbitrium levels, indicating a double-check mechanism.

Conclusions:

• A conserved SroF-Sar pair mechanism ensures phage induction under specific SOS conditions.
• A double-layer control system prevents premature phage induction, integrating host and phage signals.
• This mechanism guarantees phage induction only occurs during DNA damage and when neighboring prophages are absent.