QUORUM SENSING IN VIBRIO-FISCHERI - ESSENTIAL ELEMENTS FOR ACTIVATIONOF THE LUMINESCENCE GENES

LuxR is required for cell density-dependent activation of the Vibrio f ischeri luminescence (lux) genes. It has not been possible to study fu ll-length LuxR in vitro, but a polypeptide containing the C-terminal t ranscriptional-activator domain of LuxR (LuxR Delta N) has been purifi ed, and its binding to lux regulatory DNA has been investigated. By it self, LuxR Delta N interacts with a region of lux regulatory DNA that is upstream of the lux box, which is a 20-bp element that is required for LuxR activation of the luminescence operon. Individually, neither the purified LuxR Delta N nor RNA polymerase binds to the her box regi on, but together the two proteins bind in synergy to the lux box-luxI promoter region. We show that binding of LuxR Delta N to the upstream region is not a prerequisite for its synergistic binding with RNA poly merase to the lux box and the luxI promoter region. We also show that LuxR Delta N and RNA polymerase are both required and sufficient for t ranscriptional activation of the lux operon. This argues against the h ypothesis that LuxR functions to alleviate repression of the lux opero n by another cellular factor. Rather, our data support the view that L uxR functions as an accessory factor that enables RNA polymerase to bi nd to and initiate transcription from the promoter of the lux operon.