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Regulation
1. Overview of the various regulatory mechanisms observed in bacteria
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Regulation at the level of gene structure (inversion, flagella phase variation, or
movement of a section of DNA, degree of methylation of DNA, degree of
supercoiling).
Control at the level of transcriptional level (level of methylation, degree of
supercoiling, new sigma subunits, negative/positive regulatory proteins,
attenuation, riboswitches).
Control at the level of translation (translation initiation, mRNA stability, binding
of a metabolite to a riboswitch, antisense RNA)
Regulating the activity of a protein/enzyme (allosteric enzymes, covalent
modification).
2. Definition of constitutive, inducible, and repressible enzyme systems.
Lectures will focus on regulatory mechanisms in which the central theme is that
control is mediated by low molecular substances that are either synthesized by the cell or
present in the environment. These low MW molecules, called EFFECTOR
MOLECULES or ligands, interact with specific protein molecules, called ALLOSTERIC
PROTEINS, and alter the properties of these proteins, i.e., maltose binding protein and
MCP II.
3. The Lactose Operon (an inducible enzyme system).
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Definition of an operon
-galactosidase (lactase) required to metabolize lactose
Diauxic growth
Graduitous inducers
organization of lactose utilizing genes
Operon regulated by a negative (lac repressor) and positive (CAP- catabolite
activtor protein) regulatory protein.
Model to explain regulation at level of transcription. Lac repressor is an allosteric
protein. What does this mean?
Model to explain catabolite repression. CAP is an allosteric protein. What is its
effector molecule?
How does the maltose operon differ from the lac operon?
4. Tryptophan Operon (a repressible enzyme system).
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Trp biosynthetic pathway
Regulation at level of enzyme activity. Feedback (end-product) inhibition of
anthranilate synthetase (first enzyme committed to tryp biosynthesis) by trp.
Regulation at level of transcription.
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Tryptophan Operon. Organization of tryp genes.
Repression of operon by Tryp repress
Attentuation: premature termination of transcription in leader region due
to the state of translation of a peptide encoded within leader region.
 leader region (region between operator and first structual gene).
 162 nucleotides with a transcriptional termination site at 3' end.
 encodes for a short polypeptide chain (14 amino acid) which has
two tryp codons.
 base pairing that can occur within leader region
 impact that specific base pairing has on transcription
 model
5. Regulation of glutamine synthetase: an example of cumulative feedback inhibition and
covalent modification by adenylation.
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Assimilation of inorganic nitrogen: glutamic dehydrogenase vs. glutamine
synthetase and glutamate synthetase.
Glutamine synthetase (GS) composed of 12 identical subunits, each subunit has 8
distinct allosteric sites (96 potential allosteric sites).
To have cumulative feedback inhibition GS must be covalently modified by the
addition of an adenyl group (AMP from ATP) to each subunit. When fully
adenylated, GS is less active and more susceptible to cumulative feedback
inhibition.
Regulation of branched biosynthetic pathways (isofunctional, sequential,
concerted, and cumulative inhibition). How does concerted and cumulative
inhibition differ?
Adenylating enzyme, AMP-adenyl transferase, also removes adenyl groups! How
does cell avoid futile recycling of ATP?
Protein PII, a protein subject to covalent modification by uridyl transferase (UMP
from UTP). What controls if PII is modified or not? and how does this impact the
acitivity of GS?
6. Flagella phase variation.
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ability to switch between making two types of flagellin proteins (subunit that
makes up filament component of flagellum).
inversion of a region of DNA that contains promoter region for H2 flagellin gene
and H1 repressor.
7. Anitsense RNA’s
8. Riboswitches: Can act at level of transcription or translation
Revised 11/11/09