Transcriptional activator that functions in response to the quorum-sensing autoinducer IV-HSL (isovaleryl-homoserine lactone). Activates BjaI expression. Is sensitive to IV-HSL at concentrations as low as 10 pM. In cells lacking this gene, bjaI expression is about 15% of the level in wild-type cells and IV-HSL is <25% of wild-type levels. Belongs to the autoinducer-regulated transcriptional regulatory protein family.