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In genetics and molecular biology, a corepressor is a molecule that represses the expression of genes. [1] In prokaryotes, corepressors are small molecules whereas in eukaryotes, corepressors are proteins. A corepressor does not directly bind to DNA, but instead indirectly regulates gene expression by binding to repressors.
In the reverse reaction, histone deacetylase (HDAC) removes the acetyl group from the histone tails and binds it to coenzyme A to form acetyl-CoA. Some coactivators indirectly regulate gene expression by binding to an activator and inducing a conformational change that then allows the activator to bind to the DNA enhancer or promoter sequence.
In molecular biology and genetics, transcription coregulators are proteins that interact with transcription factors to either activate or repress the transcription of specific genes. [1] Transcription coregulators that activate gene transcription are referred to as coactivators while those that repress are known as corepressors .
The ability of nuclear receptors to alternate between activation and repression in response to specific molecular cues, is now known to be attributable in large part to a diverse group of cellular factors, collectively termed coregulators and including coactivators and corepressors.
Diagram of mediator with cyclin-dependent kinase module. Mediator is a multiprotein complex that functions as a transcriptional coactivator in all eukaryotes.It was discovered in 1990 in the lab of Roger D. Kornberg, recipient of the 2006 Nobel Prize in Chemistry.
In molecular biology, an inducer is a molecule that regulates gene expression. [1] An inducer functions in two ways; namely: By disabling repressors. The gene is expressed because an inducer binds to the repressor. The binding of the inducer to the repressor prevents the repressor from binding to the operator.
Response to stimuli: a response can take many forms, from the contraction of a unicellular organism to external chemicals, to complex reactions involving all the senses of multicellular organisms. A response is often expressed by motion; for example, the leaves of a plant turning toward the sun (phototropism), and chemotaxis.
The sources for these mutations can be errors during replication, spontaneous mutations, and chemical and physical mutagens (UV and ionizing radiation, heat). [10] Silencers, being encoded in the genome, are susceptible to such alterations which, in many cases, can lead to severe phenotypical and functional abnormalities.