Zusammenfassung
Transcriptional control under nitrogen and carbon-limitation conditions
have been well analyzed for Escherichia colt. However, the
transcriptional dynamics that underlie the shift in regulatory programs
from nitrogen to carbon limitation is not well studied. In the present
study, cells were cultivated at steady state under nitrogen
(ammonia)-limited conditions then shifted to carbon (glucose) limitation
to monitor changes in transcriptional dynamics. Nitrogen limitation was
found to be dominated by sigma 54 (RpoN) and sigma 38 (RpoS), whereas
the ``housekeeping'' sigma factor 70 (RpoD) and sigma 38 regulate
cellular status under glucose limitation. During the transition,
nitrogen-mediated control was rapidly redeemed and mRNAs that encode
active uptake systems, such as ptsG and manXYZ, were quickly amplified.
Next, genes encoding facilitators such as lamB were overexpressed,
followed by high affinity uptake systems such as mglABC and non-specific
porins such as ompF. These regulatory programs are complex and require
well-equilibrated and superior control. At the metabolome level,
2-oxoglutarate is the likely component that links carbon- and
nitrogen-mediated regulation by interacting with major regulatory
elements. In the case of dual glucose and ammonia limitation, sigma 24
(RpoE) appears to play a key role in orchestrating these complex
regulatory networks.
Nutzer
