UV induction of coliphage 186: prophage induction as an SOS function

Area of Science:

• Microbiology
• Molecular Biology
• Bacteriophage Genetics

Background:

• Bacteriophages, like coliphage 186, can integrate into host genomes as prophages.
• Prophage induction, often triggered by DNA damage (e.g., UV irradiation), leads to phage replication and host cell lysis.
• The regulatory mechanisms of prophage induction vary among different phage types.

Purpose of the Study:

• To investigate the mechanism of UV induction for the 186 prophage.
• To identify the specific phage and host factors involved in 186 prophage induction.
• To compare the induction pathway of coliphage 186 with other UV-inducible phages.

Main Methods:

• Analysis of mutant phenotypes (turbid plaques) on mitomycin plates.
• Characterization of phage gene expression, specifically the Tum function.
• Investigation of host LexA protein control over phage gene expression.
• Sequence analysis to identify regulatory elements like LexA-binding sites.

Main Results:

• UV induction of the 186 prophage is dependent on the phage function Tum.
• The expression of Tum is controlled by the host LexA protein.
• A sequence resembling the LexA-binding site overlaps the Tum promoter (p95).
• Inactivation of LexA, either by UV or genetic means, allows Tum expression, leading to prophage induction.

Conclusions:

• A novel mechanism for UV-inducible prophage induction is proposed for coliphage 186, involving the Tum function and LexA regulation.
• This pathway is distinct from the induction mechanisms of UV-inducible lambdoid coliphages, which are not LexA-regulated.
• The findings highlight the diversity of prophage regulatory strategies in bacteria.