Gene Regulation in Prokaryotes

Gene Regulation in Prokaryotes

Gene transcription does not occur at a constant rate. Genes can either be turned "on" (with transcription occurring at a relatively high rate) or "off" (transcription occurs at a very low rate). The problems in this unit ask you to reason about the behavior of the regulatory systems that control gene expression in bacteria.

Regulatory System Components

These regulatory systems have multiple components:

One. A structural gene that codes for an enzyme. This is the gene whose activity is being controlled. For instance, in E. coli the LacZ gene codes for an enzyme beta-galactosidase that metabolizes lactose.

Two. A regulatory gene that codes for a regulatory protein that, in conjunction with an effector molecule described below, controls transcription of the structural gene. (In E. coli, the LacI gene codes for the regulatory protein LacR, which controls transcription of LacZ.)

Three. An operator gene, which is a sequence of DNA adjacent to the structural gene on the chromosome. The regulatory protein binds to the operator to control expression of the structural gene. (In E. coli, the Lack regulatory protein binds to the LacO operator site.)

Four. An effector is a small molecule that binds to the regulatory protein to govern the activity of the regulatory protein. For instance, lactose itself is the small molecule that binds with the regulatory protein LacR in E. coli to control transcription of the LacZ gene.