Gene regulation in Archaea
Lrp-like transcriptional regulators from Sulfolobus sp.
Archaea are true prokaryotes, but they constitute a separate domain of life and are very different from bacteria. The archaeal information processing machineries are even more closely related to the eukaryal homologs than to the bacterial ones. The multi-subunit composition of the unique archaeal RNA polymerase is most reminiscent of eukaryal Pol II. In contrast, archaeal transcription regulators appear to be mostly of the bacterial type. Their mode of action is however still poorly investigated. We focus on transcriptional regulators of the Lrp-like family (leucine responsive regulatory protein) from Sulfolobus acidocaldarius and S. solfataricus, two aerobic, sulfur-dependent hyperthermoacidophilic crenarchaeota which grow optimally at 80°C and pH 2-3. The genome sequences have been determined and Sulfolobus has developed into an important model organism for molecular, biochemical and pioneering genetic studies on hyperthermophilic crenarchaeota. Recently we have demonstrated cooperative binding of Ss-LrpB to three targets in its own control region. This binding induces profound structural deformations (bending). Therefore, complex formation relies on protein-DNA and protein-protein interactions and on DNA conformability. Based on our in vitro binding assays we have proposed a model for the autoregulatory process that is based on a switch from positive autoregulation at low protein concentration to a negative autoregulation at high protein concentration. Now, we focus on the structure -function relationship in Ss-LrpB (mutant analyses), on structural aspects of the Ss-LrpB protein and of Ss-LrpB-operator complexes (Atomic Force Microscopy, crystallography), on functional aspects of the regulatory process (inhibition/stimulation) and on the physiological role of Ss-LrpB. An in silico screening of the genome sequence has revealed the presence of several potential targets for Ss-LrpB which are now being experimentally tested for binding.