Bacteria employ a diverse array of cellular regulatory
mechanisms to successfully adapt and thrive in ever-changing
environments, including but not limited to temperature
changes, fluctuations in nutrient availability, the presence
or absence of electron acceptors such as oxygen, the availability
of metal ions crucial for enzyme activity, and the
existence of antibiotics. Bacteria can virtually modulate
any step of gene expression from transcr!ptional initiation
to posttranslational modification of a protein for the control
of cellular processes. Furthermore, one gene regulator
often controls another in a complex gene regulatory network.
Thus, it is not easy to fully understand the intricacies of
bacterial regulatory mechanisms in various environments. In
this special issue, while acknowledging the challenge of covering
all aspects of bacterial regulatory mechanisms across
diverse environments, seven review articles are included to
provide insight into the recent progress in understanding
such mechanisms from different perspectives: positive regulatory
mechanisms by secondary messenger (cAMP receptor
protein), two-component signal transduction mechanisms
(Rcs and Cpx), diverse regulatory mechanisms by a specific
environmental factor in specific bacteria (oxygen availability
in Mycobacterium and manganese ion availability in Salmonella),
diverse regulatory mechanisms by a specific environmental
factor (temperature and antibiotics), and regulatory
mechanisms by antibiotics in cell wall synthesis.
Bacteria, as ubiquitous organisms that can be found in
almost every environment, carry out complex cellular processes
that allow them to survive and thrive in a variety of
different conditions despite their small size and relative simplicity.
One of the key factors that allows bacteria to carry
out these complex processes is their ability to regulate gene
expression through various mechanisms. Gene expression
is a fundamental biological process by which the genetic
information encoded in a gene is transcribed into an RNA
molecule and subsequently translated into a functional gene
product, often a protein. Furthermore, the activity levels of
proteins may further be altered by posttranslational modification.
Regulation of gene expression refers to the control
of the amount and timing of gene expression, and thus it
can be divided into transcr!ptional, translational, and posttranslational
levels.
A reducing system of SoxR, a regulator of redox-active molecules,
was identified as rsxABCDGE gene products and RseC
in Escherichia coli through genetic studies. We found that
ApbE was an additional component of the reducer system.
Bacterial two hybrid analysis revealed that these proteins indeed
had multiple interactions among themselves. RseC and
RsxB formed the core of the complex, interacting with more
than five other components. RsxC, the only cytoplasmic component
of the system, interacted with SoxR. It might be linked
with the rest of the complex via RsxB. Membrane fractions
containing the wild type complex but not the mutant complex
reduced purified SoxR using NADH as an electron source.
These results suggest that Rsx genes, RseC, and ApbE can
form a complex using NAD(P)H to reduce SoxR.