Quorum sensing in Vibrio fischeri: Analysis of the LuxR DNA binding regionby alanine-scanning mutagenesis

LuxR is the transcriptional activator for quorum-sensing control of lumines cence in Vibrio fischeri. A series of alanine-scanning mutants spanning a p redicted helix-turn-helix region in the DNA binding domain of LuxR was cons tructed, and the activity of each of the LuxR mutant proteins in recombinan t Escherichia call was investigated. The region covered by the mutagenesis spanned residues 190 to 224. About half of the alanine-scanning mutants sho wed activities similar to that of the wild-type LuxR: at least two were pos itive-control mutants, four appeared to be defective in DNA binding, and se veral others were characterized as DNA binding affinity mutants. This analy sis, taken together with information about other bacterial transcription fa ctors, provides insights into amino acid residues in LuxR that are involved in DNA binding and transcriptional activation.