Promoter (genetics)

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1: RNA Polymerase, 2: Repressor, 3: Promoter, 4: Operator, 5: Lactose, 6: lacZ, 7: lacY, 8: lacA.
Top: The gene is turned off. There is no lactose to inhibit the repressor, so the repressor binds to the operator. This stops the RNA polymerase from binding to the promoter and making lactase.
Bottom: The gene is turned on. Lactose inhibits the repressor. This allows the RNA polymerase to bind with the promoter, and express the genes. The genes now synthesize lactase. Eventually, the lactase will digest all of the lactose, until there is none to bind to the repressor. The repressor will then bind to the operator, stopping the manufacture of lactase.

In genetics, a promoter is a region of DNA that starts transcription of a particular gene.

Promoters are near the genes they transcribe, on the same strand of DNA and upstream.

Promoters can be about 100–1000 base pairs long.[1]

Overview[change | change source]

For the transcription to take place, the enzyme that makes RNA, known as RNA polymerase, must attach to the DNA near a gene.

Promoters contain specific DNA sequences which give the RNA polymerase a binding site. There are also a number of proteins which help this process along, or which stop it happening. The whole thing is called the regulation of gene expression.

In bacteria
The promoter is recognized by RNA polymerase and an associated protein.
In eukaryotes
The process is more complicated, and at least seven different factors are necessary for the binding of an RNA polymerase II to the promoter.

Promoters are critical elements which work in concert with other regulatory regions. Together they adjust the level of transcription of a gene. So, genes get switched on when they are needed, and switched off when they are not. When they are on, they get adjusted up or down as needed.

References[change | change source]