Transcriptional Regulation

The first step of gene regulation, is transcription regulation. It is achieved by transcription factors that control how much RNA will be produced. They will either help or or hinder RNA polymerase binding to DNA.

Transcription Factor (TF)

A protein that binds to a specific DNA sequences, hence controlling the rate of transcription. It will either block (as a repressor) or recruit (as an activator) RNA polymerase, which is the enzyme that does transcription.

Transcription factors contain DNA-binding domains.

Promoter

A promoter is a region in DNA that initiates transcription of a gene.

As known as gene promoter.

Promoter (genetics) [wikipedia.org].

Usually this is near the transcription start site.

Enhancer

Short regions of DNA, between 50-1500 bp long, that can be located up to 1M bp away from a gene. Activators will bind to these, recruit mediators, finally RNA polymerase, and then transcription will start.

Enhancer (genetics) [wikipedia.org]..

Silencer

Short regions of DNA that repressors bind to. Once the repressor binds to the silencer, RNA polymerase and another transcription factors are unable to bind to the promoter region.

With transcription blocked, DNA cannot be transcribed, so gene expression is lower.

Silencer (DNA) [wikipedia.org].

Repressor

The lac repressor binds to the silencer in bacteria and stops the lactose proteins from being expressed.

When no lactose is present, the lac repressor is bound to the DNA silencer.

When lactose is present, lactose binds to the lac repressor, causing an allosteric change. After the lac repressor shape has change, it unbinds from the DNA, allowing transcription.

Lac repressor [wikipedia.org].

Activator

Heat shock factors (HSF) are transcriptional activators of heat shock genes. They bind to the heat shock element (HSE) promoter. HSF-1 is a regulator for HSE in eukaryotes, in normal temperature (absence of stress), it is inhibited as it bound to heat shock proteins. When temperature increases, other proteins misfold, and heat shock proteins bind to misfolded proteins, and dissociate from HSF-1. HSF-1 is now free to bind to the HSE and activate transcription.

Transcription Factor Binding Sites motifs

Binding sites are short, conserved, but degenerative DNA motifs of 6-15 bp.

Variability allows binding of TFs with different affinity, affecting transcription, leading to differential gene expression.