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In genetics and cell biology, repression is a mechanism often used to decrease or inhibit the expression of a gene. Removal of repression is called derepression. This mechanism may occur at different stages in the expression of a gene, with the result of increasing the overall RNA or protein products.
In 1986–1990, multiple examples of "coat protein-mediated resistance" against plant viruses were published, before RNAi had been discovered. [40] In 1993, work with tobacco etch virus first demonstrated that host organisms can target specific virus or mRNA sequences for degradation, and that this activity is the mechanism behind some examples ...
In general terms, mutations in silencer elements or regions could lead to either the inhibition of the silencer's action or to the persisting repression of a necessary gene. This can then lead to the expression or suppression of an undesired phenotype which may affect the normal functionality of certain systems in the organism.
RNA interference (RNAi) is a biological process in which RNA molecules are involved in sequence-specific suppression of gene expression by double-stranded RNA, through translational or transcriptional repression. Historically, RNAi was known by other names, including co-suppression, post-transcriptional gene silencing (PTGS), and quelling. The ...
The above mechanism of repression is a type of a feedback mechanism because it only allows transcription to occur if a certain condition is present: the presence of specific inducer(s). In contrast, an active repressor binds directly to an operator to repress gene expression.
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.
For example, miR16 contains a sequence complementary to the AU-rich element [90] found in the 3'UTR of many unstable mRNAs, such as TNF alpha or GM-CSF. [91] It has been demonstrated that given complete complementarity between the miRNA and target mRNA sequence, Ago2 can cleave the mRNA and lead to direct mRNA degradation.
Intragenic suppression results from suppressor mutations that occur in the same gene as the original mutation. In a classic study, Francis Crick (et al.) used intragenic suppression to study the fundamental nature of the genetic code. From this study it was shown that genes are expressed as non-overlapping triplets . [1]