Chapter 18- Control of Gene Expression in Bacteria 

18.1 An Overview of Gene Regulation and Information Flow

• The flow of information from DNA to active protein suggest three possible mechanisms:

  • Transcriptional control: The cell could make mRNAs only for proteins it needs.

  • Translational control: The cell could prevent the mRNAs for unneeded proteins from being translated.

  • Post-translational control: After translation, many proteins have to be activated by chemical modification, such as the addition of a phosphate group, in order to function.

• An inducer is a small molecule that triggers transcription of a specific gene.

18.2 Negative and Positive Control of Transcription

• Negative control occurs when a regulatory protein called a repressor binds to DNA and shuts down transcription

• Positive control occurs when a regulatory protein called an activator binds to DNA and triggers transcription

• Cells that are abnormal because they produce a product at all times instead of regulating expression of the product are called constitutive mutants.

• Jacob and Monod coined the term operon to describe a set of coordinately regulated bacterial genes that are transcribed together into one polycistronic mRNA.

• The group of genes involved in lactose metabolism was termed the lαc operon.

• The repressor binds to a DNA sequence in the lαc operon called the operator.

• In allosteric regulation, a small molecule binds to a protein and causes it to change its shape and activity.

• A protein known as the catabolite activator protein (CAP) has long been viewed as exerting positive control of many operons in E. coli, including the lαc operon.

• Negative feedback control is a form of control in which the final product of a pathway inhibits the production of the product.

• The only difference is that for the trp operon the small molecule regulator is called a co-repressor, because it works with the repressor to make it active.

18.3 Global Gene Regulation

• Global gene regulation is the coordinated regulation of many genes.

• Regulon is a set of separate genes and operons at contain the same regulatory sequences and are controlled by a single type of regulatory protein

• A key part of the regulatory logic of the SOS system is that it is under the control of one of its own genes.