Repressor


Repressor

:"For other uses, see repression"A repressor is a DNA-binding protein that regulates the expression of one or more genes by decreasing the rate of transcription. This blocking of expression is called repression.

Repressor proteins are coded for by regulator genes. Repressor proteins then attach to a DNA segment known as the operator. By binding to the operator, the repressor protein prevents the RNA polymerase from creating messenger RNA.

If an inducer, a molecule that initiates the gene expression, is present, then it can interact with the repressor protein and detach it from the operator. RNA polymerase then can transcribe the message (expressing the gene). A corepressor is a molecule that can bind to repressor and make it binds to operator tightly, which decreases transcription.

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).

Examples

An example of a repressor protein is the methionine repressor MetJ. MetJ is a homodimer consisting of two monomers which each provide a beta ribbon and an alpha helix. Together, the beta ribbons of each monomer come together to form an antiparallel beta-sheet which binds to the DNA operator ("Met box") in its major groove. Once bound the MetJ dimer interacts with another MetJ dimer bound to the complementary strand of the operator via its alpha helices.

The Met box has the sequence AGACGTCT which is a palindrome (it shows dyad symmetry) allowing the same sequence to be recognised on either strand of the DNA. The junction between c and g in the middle of the Met box contains a pyramidine-purine step that becomes over-twisted forming a kink in the phosphodiester backbone. This is how the protein checks for the recognition site as it allows the DNA duplex to follow the shape of the protein.

Each MetJ dimer contains two binding sites for the cofactor S-Adenosyl methionine (SAM) which is a product in the biosynthesis of methionine. When SAM is present it binds to the MetJ protein increasing its affinity for its cognate operator site which halts transcription of genes involved in methionine synthesis. When SAM concentration becomes low the repressor dissociates from the operator site allowing more methionine to be produced.

ee also

* lac repressor

External links

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Look at other dictionaries:

  • repressor — repressor. См. репрессор. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • Repressor — Repressor, vom ⇒ Regulatorgen codiertes, die Aktivität des ⇒ Operators regulierendes Protein in Protocyten; dient der ⇒ Genregulation bei Prokaryoten, wie sie durch das ⇒ Jacob Monod Modell beschrieben ist …   Deutsch wörterbuch der biologie

  • repressor — |ô| adj. s. m. Que ou aquele que reprime …   Dicionário da Língua Portuguesa

  • repressor — [ri pres′ər] n. something that represses; esp., a protein produced in a cell that prevents the synthesis of a specific enzyme: also sp. represser …   English World dictionary

  • Repressor — Als Repressor bezeichnet man in der Genetik ein DNA bindendes Regulator Protein, welches an den Operator bindet und damit die Bindung der RNA Polymerase an den Promotor blockiert, wodurch die Transkription des Gens (oder Operons) verhindert wird …   Deutsch Wikipedia

  • repressor — represorius statusas T sritis augalininkystė apibrėžtis Reguliuojančiojo geno koduojamas baltymas, kuris stabdo geno operatoriaus veiklą ir dėl to įsijungia operonas. atitikmenys: angl. repressor rus. репрессор …   Žemės ūkio augalų selekcijos ir sėklininkystės terminų žodynas

  • repressor — noun Etymology: New Latin Date: 1611 one that represses; especially a protein that is determined by a regulatory gene, binds to a genetic operator, and inhibits the initiation of transcription of messenger RNA …   New Collegiate Dictionary

  • repressor — /ri pres euhr/, n. 1. represser. 2. Genetics. a protein that binds DNA at an operator site and thereby prevents transcription of one or more adjacent genes. [1955 60; < L; see REPRESS, TOR] * * * …   Universalium

  • repressor — noun a) Anything that represses. b) Any protein that binds to DNA and thus regulates the expression of genes by decreasing the rate of transcription …   Wiktionary

  • repressor — The product of a regulator or r. gene. active r. a r. that combines directly with an operator gene to repress the operator and its structural genes, thus repressing protein synthesis; an active r. may be repressed by an …   Medical dictionary