Separating Functions of the Phage-Encoded Quorum-Sensing-Activated Antirepressor Qtip

Summary Quorum sensing is a process of chemical communication that bacteria use to track cell density and coordinate gene expression across a population. Bacteria-infecting viruses, called phages, can encode quorum-sensing components that enable them to integrate host cell density information into the lysis-lysogeny decision. Vibriophage VP882 is one such phage, and activation of its quorum-sensing pathway leads to the production of an antirepressor called Qtip. Qtip interferes with the prophage repressor (cI VP882 ), leading to host-cell lysis. Here, we show that Qtip interacts with the N-terminus of cI VP882 , inhibiting both cI VP882 DNA-binding and cI VP882 autoproteolysis. Qtip also sequesters cI VP882 , localizing it to the poles. Qtip can localize to the poles independently of cI VP882 . Alanine-scanning mutagenesis of Qtip shows that its localization and interference with cI VP882 activities are separable. Comparison of Qtip to a canonical phage antirepressor reveals that, despite both proteins interacting with their partner repressors, only Qtip drives polar localization.