Butyrolactone autoregulator receptor protein (BarA) as a transcriptional regulator in Streptomyces virginiae

BarA of Streptomyces virginiae is a specific receptor protein for virginiae butanolides (VBs), a member of the butyrolactone autoregulators of Streptomyces species. Sequencing around the barA gene revealed two novel open reading frames: one upstream, barX, encoding a homolog of AfsA of Streptomyces griseus and another downstream, barB. Northern (RNA) blot analysis for S. virginiae demonstrated that the addition of VB during cultivation switched on the expression of barB. An in vivo expression system in Streptomyces lividans with the use of the xylE reporter gene indicated that BarA in conjunction with VB controlled the barB promoter. Furthermore, the DNA binding ability of BarA was demonstrated in vitro for the first time by means of surface plasmon resonance and a gel-shift assay. Complex formation with VB in vitro resulted in the dissociation of BarA from DNA, thus suggesting that the VB receptor, BarA, is a transcriptional regulator and that the VB signal is transduced to the next step in the signal transduction pathway by modification of the DNA binding ability of BarA.