SYNERGISTIC BINDING OF THE VIBRIO-FISCHERI LUXR TRANSCRIPTIONAL ACTIVATOR DOMAIN AND RNA-POLYMERASE TO THE LUX PROMOTER REGION

LuxR, the Vibrio fischeri luminescence gene (lux) activator, is the be st-studied member of a family of bacterial transcription factors requi red for cell density-dependent expression of specific genes involved i n associations with eukaryotic hosts. Neither LuxR nor any other LuxR homolog has been shown to bind DNA directly. We have purified the LuxR C-terminal transcriptional activator domain from extracts of recombin ant Escherichia coli in which this polypeptide was expressed. The puri fied polypeptide by itself binds to lux regulatory DNA upstream of the lux box, a 20-bp palindrome that is required for LuxR activity in viv o, but it does not bind to the lux box. However, the LuxR C-terminal d omain together with RNA polymerase protects a region including the lux box and the lux operon promoter from DNase I cleavage. There is very little protection of the lux operon promoter region from DNase I diges tion in the presence of RNA polymerase alone. Apparently, there is a s ynergistic binding of the LuxR C-terminal domain and RNA polymerase to the promoter region. The upstream binding region for the purified pol ypeptide encompasses a binding site for cAMP receptor protein (CRP). U nder some conditions, CRP binding can block the binding of the LuxR C- terminal domain to the upstream binding region, and it can also block the synergistic binding of the LuxR C-terminal domain and RNA polymera se to the lux box and luminescence gene promoter region. This descript ion of DNA binding by the LuxR C-terminal domain should lead to an und erstanding of the molecular interactions of the LuxR family of transcr iptional activators with regulatory DNA.