Controlling transcription
Transcription factors are regulatory proteins that alter whether particular genes are transcribed. In eukaryotic cells, specific factors can pass from the cytoplasm into the nucleus through nuclear pores.
A transcription factor can interact with DNA associated with its target gene. One important regulatory region is the promoter, located before the coding sequence and involved in controlling whether transcription takes place.
A stimulatory factor can help RNA polymerase associate with the promoter, whereas an inhibitory factor can prevent effective RNA polymerase binding. Transcription of the target gene therefore rises or falls according to the regulatory factor involved.
Stimulation and inhibition
| Action | Effect on the target gene |
|---|---|
| Stimulation | RNA polymerase is helped to associate with the promoter, increasing transcription of the target gene. |
| Inhibition | RNA polymerase is prevented from binding effectively, reducing or preventing transcription of the target gene. |
If the target is a protein-coding gene, altering its transcription changes the quantity of mRNA made and can consequently change how much of the corresponding protein is produced.
Exam Tip: State whether the factor causes stimulation or inhibition, then connect this to RNA polymerase binding, the amount of mRNA formed and the resulting effect on protein production.