LuxR-type proteins are responsible for density-dependent transcriptional regulation in quorum-sensing systems that employ acyl-homoserine lactones (acyl-HSLs) as signal molecules. The Vibrio fischeri lux operon, which includes LuxR, has been well studied and shown to function in E. coli. The components of the lux operon have been used to engineer de novo genetic circuits because they provide a versatile intercellular communications system. We have used directed evolution to engineer LuxR to generate new components for engineering...