Regulation of early gene expression in the temperate lactococcal phage TP901-1
Special Symposium - Innovations in Food Technology (LMC Congress)
Innovations in Food Technology - Poster Session (LMC/Food - P1)
Keywords: Lactococcus, bacteriophage, switch
Bacteriophages are viruses that infect bacteria and use the host to generate new phage progeny. Infection of starter cultures by bacteriophages poses a major problem in the dairy industry and influences the quality of the finished products. Thus, numerous studies have been performed with lactococcal phages.
After infection of a sensitive host by a temperate phage such as the lactococcal phage TP901-1, the phage chooses to enter either a lytic or a lysogenic lifecycle. In the lytic lifecycle new phage progeny is produced and released to the surroundings following cell lysis, whereas in the lysogenic lifecycle the viral genome remains dormant within the host cell. A genetic switch controlling transcription of two different sets of genes regulates the choice between these two different lifecycles. The genetic switch of the temperate phage TP901-1 is the best studied among lactococcal phages. Two divergently oriented promoters; PL (lytic) and PR (lysogenic), recognized by the host RNA polymerase are responsible for transcription of the early gene clusters in the TP901-1 genome. Initiation of transcription from both PL and PR is regulated by the TP901-1 repressor, CI, in consort with the modulator of repression, MOR. It has been suggested that during early lytic infection MOR functions as an anti-repressor that interacts with CI thereby preventing binding of CI to the operator sites. We have shown that mor encodes a protein and that this protein is required for the choice between the two different lifecycles.
In order to get further insight into the mechanism of action of the phage encoded CI protein we constructed specific mutations and C-terminal deletions in the TP901-1 repressor and studied the effects in vivo. The obtained data were combined with in vitro experiments, where we over-expressed and purified mutated or truncated forms of the TP901-1 repressor. We identified the N-terminal part of the TP901-1 repressor as the DNA binding domain and the C-terminal part of the protein as being responsible for oligomerization. For the first time, we show the overall structure of a full-length wild type bacteriophage repressor in solution, and reveal that the TP901-1 repressor forms a flat disc-like structure.
Presented Wednesday 19, 13:30 to 15:00, in session Innovations in Food Technology - Poster Session (LMC/Food - P1).
