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Gene expression is regulated at many levels in bacteria. Figure 14.1 in your textbook displays a
summary of regulatory mechanisms used to control gene expression. The expression of bacterial
genes is controlled by the action of diffusible repressors and activators. Tetracycline is an
antibiotic used to treat respiratory infections, infections of the skin, including acne, and
infections of the genitourinary system. Over time however, many bacteria have become resistant
to tetracycline. The mechanism often utilized by resistant strains is the synthesis and use of an
efflux pump. While there are multiple types, in general, this pump consists of a membrane‐
spanning protein that extrudes the antibiotic from the cell. Since efflux pumps are energetically
expensive to make, they are only produced when tetracycline is present. A repressor protein,
TetR, has been identified and characterized in resistant strains. The efflux‐pump
is negatively controlled by TetR. TetR binds to the operator region when there is no tetracycline
available. When tetracycline is present, TetR is released from the DNA. TetR gene transcription
is inhibited by the repressor protein. We can also look at an example of positive control.
Regulatory proteins can bind to activator binding sites in the presence of a key nutrient or other
chemical in the cell. The cell is “sensing” the presence of this nutrient and the activator can then
turn on genes in response. This is the case with the transcription of fimbriae genes in some
pathogens. In order to conserve resources, fimbrial genes are only transcribed when the pathogen
is in the nutrient rich environment of the host where the amino acid leucine is abundant. Under
these conditions, the pathogen develops fimbriae and attaches itself to the epithelium of the host.
For this discussion you characterize a transcriptional regulatory system like the ones just
described. However, for our purposes this should be entirely fictional. You can even invent your
own bacterial species!!
In your initial discussion board post, please include the following:

Make up an operon, the regulatory proteins, the cellular process and the molecules being
Describe your fictional operon with legitimate details about the orientation of the genes
and the promoter/operator sequences or activator binding site.
Provide details about the repressor/activator and inducer/inhibitor proteins.
Explain how the operon helps your pathogen survive and possibly thrive in its host.
Include details about conditions that trigger expression of the gene(s).

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