What are four ways transcription is repressed?

Answer 1

Transcriptional repression can happen by four different mechanisms.

The first method involves competition between transcriptional activators and repressors for binding to DNA. A DNA binding site can either be bound by a transcriptional activator or repressor. For example, binding of a transcriptional repressor to an enhancer element will block the binding of a transcriptional activator.

The second method gives rise to transcriptional activators and repressors to bind to different DNA sequences. Transcription can be blocked if the transcriptional repressor can physically bind to the activator and thereby blocks its activity.

The third method describes the direct physical contact between the transcriptional repressor and the mediator complex. The mediator complex is unable to phosphorylate RNA Polymerase II.

The fourth method is shown by the transcriptional repressor recruiting the HDAC proteins. As a result, the acetyl groups are removed from histone proteins. This increases the positive charge on the core histones. This tightens the grip they have on DNA.

Answer 2

1. Transcriptional repressors: Proteins that bind to specific DNA sequences near the promoter region of a gene and block the binding of transcription factors and RNA polymerase, preventing transcription initiation.
2. Chromatin remodeling: Repressive chromatin modifications, such as DNA methylation or histone deacetylation, can make the DNA inaccessible to transcription machinery, hindering transcription initiation.
3. Transcriptional interference: Overlapping or nearby transcriptional events can interfere with each other, leading to the repression of one or both transcription processes.
4. RNA-mediated repression: Certain non-coding RNA molecules can bind to mRNA transcripts, inhibiting their translation and subsequently repressing gene expression at the post-transcriptional level.