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.