Ss-LrpB, a transcriptional regulator from Sulfolobus solfataricus, regulates a gene cluster with a pyruvate ferredoxin oxidoreductase-encoding operon and permease genes.

Ss-LrpB is an Lrp-like transcriptional regulator from Sulfolobus solfataricus. Previously, in vitro binding of Ss-LrpB to the control region of its own gene has been extensively studied. However, nothing was known about the physiological role of this regulator yet. Here, using the knowledge of the DNA-binding sequence specificity of Ss-LrpB, several potential binding sites were predicted in silico in promoter regions of genes located adjacently to the Ss-lrpB gene. These genes include an operon encoding a pyruvate ferredoxin oxidoreductase (porDAB) and two genes encoding putative permeases. In vitro protein-DNA interaction studies allowed the identification of the Ss-LrpB binding sites in the cognate control regions. Intriguingly, the binding site organization in the por operator is identical to that in the Ss-lrpB control region. An Ss-lrpB gene disruption mutant was constructed and the gene expression of the above-mentioned targets in this mutant was analysed by qRT-PCR and compared with isogenic wild type. Our data demonstrate that in vivo Ss-LrpB acts as an activator at the promoters of the three predicted targets. Based on these results, it appears that not all regulators belonging to the archaeal Lrp family perform a function related to the amino acid metabolism, unlike the bacterial Lrp-like regulators.