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I know about enhancers and the mechanism that lead them to increase the gene expression of their targets but I was wondering if similarly DNA repressors exist. I know about protein repressors but I am looking for some kind of anti(or reversed)-enhancer equivalent in the genome which would act like an enhancer but reduce gene expression.

I am aware of repressed/poised enhancers which would kind of be that process, even if not really a pure repression of the target gene but rather a "non-overexpression". I also know about insulators but again this would be a different mechanism.

Some intergenic region binding protein repressors which by a folding mechanism similar to enhancers would repress a gene perhaps?

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  • $\begingroup$ To my best knowledge DNA enhancers are bound by proteins, thus enhancing activity is actually carried out by the activator proteins not the DNA itself. If I get your question well you're asking if similar sequences exist but with inverse effect? Am I right? $\endgroup$ – Nandor Poka Mar 13 '15 at 8:22
  • $\begingroup$ @poka.nandor You are exactly right. $\endgroup$ – cagliari2005 Mar 13 '15 at 8:24
  • $\begingroup$ OK, thx I just wanted to make sure I do not misinterpret your question and end up having a bad, irrelevant answer. I'll look into it:) $\endgroup$ – Nandor Poka Mar 13 '15 at 8:27
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Yes, these sequences exist and they are called "silencers" (surprising, right?). There are different mechanisms by which this silencing of genes can happen.

In the "classical" way the silencer is bound by a transcription factor which either passively suppress the gene by hindering the binding of specific transcription factors or by actively preventing the assembly of the general transcription factors. See the figure from paper 1:

enter image description here

Additionally there are non-classical negative regulatory element (NRE), which are usually elements upstream of the promoter which inhibit the binding regulatory proteins. NRE can also be enhancers depending on the proteins bound on them. Some NRE can induce a bend of the DNA, inhibiting the access to enhancer or promoter elements.

References:

  1. Transcriptional control and the role of silencers in transcriptional regulation in eukaryotes.
  2. Transcriptional Regulatory Elements in the Human Genome
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    $\begingroup$ Thanks! How did I forgot about them I don't know :) $\endgroup$ – cagliari2005 Mar 13 '15 at 17:40

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