AUTOREGULATION OF LUXR - THE VIBRIO-HARVEYI LUX-OPERON ACTIVATOR FUNCTIONS AS A REPRESSOR

Mobility-shift assays have been used to demonstrate that the activator of the Vibrio harveyi lux operon, LuxR, binds independently, and with similar affinity, to two sites upstream of its own open reading frame . One site was located between 52 and 107 bp upstream of, and the othe r site in a region 25 bp downstream of, the transcriptional start site . The luxR promoter, in a transcriptional fusion with the chlorampheni col acetyl transferase (cat) gene, could readily be expressed in Esche richia coli as well as V. harveyi in the absence of LuxR. In both spec ies, the presence of the luxR gene product resulted in repression of l uxR promotion. These results show that LuxR directly regulates its own expression by functioning as an autorepressor. A mechanism for this r epression is suggested by evidence showing that LuxR has a negative ef fect on RNA polymerase binding to the luxR promoter. In light of the f act that LuxR is also part of a regulatory family of repressors, the m echanism by which LuxR functions as a transcriptional activator of the lux operon has been re-examined.