Another engineering principle: Characterization. A stupid engineering joke:. A physicist, a mathematician and an engineer were each asked to establish the volume of a red rubber ball.
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Turn gene(s) on/off
Proteins to deal with
structured domains connected by more flexible domains, leading to different functions
Start site of txn is +1
α α ββ’σ
-10 and -35 sequences
Deviation from consensus -10 , -35 sequence leads to
weaker gene expression
Extreme heat shock, unfolded proteins
E. coli can choose between 7 sigma factors and about 350
transcription factors to fine tune its transcriptional output
An Rev Micro Vol. 57: 441-466T. M. Gruber
Cofactor binding alters conformation
Binds more stably than either protein alone
DNA of lac control region
CAP = catabolite
CRP = cAMP receptor
•another example of operon that has both positive
and negative regulation
•araB, A, and D encode the 3 arabinose
•araC encodes the control protein AraC which is both
a positive regulator (in the presence of arabinose) and
a negative regulator (in the absence of arabinose).
•cAMP-CAP complex also acts as a positive regulator
•When arabinose is absent, the AraC protein acts as
a negative regulator.
•AraC acts as a dimer, and causes the DNA to loop.
Looping brings the I1 and O2 sites in proximity to one
•One AraC monomer binds to I1 and a second monomer
binds to O2.
•Binding of AraC prevents RNA Pol from binding to
the PBAD promoter
•When arabinose is present, it binds to AraC and changes
•An arabinose-AraC dimer complex binds preferentially
to I1 and I2, and NOT to O2 which causes ‘opening’
of the loop. This allows RNA Pol to bind to PBAD.
•If glucose levels are low, cAMP-CAP complex binds
•Active transcription occurs.