A-Describe the mechanics by which an activator may directly increase transcripti
ID: 164906 • Letter: A
Question
A-Describe the mechanics by which an activator may directly increase transcription of target gene?B -Explain how two or more activitor may act synergistically to activate transcription by the mechanisms discribed in a ? A-Describe the mechanics by which an activator may directly increase transcription of target gene?
B -Explain how two or more activitor may act synergistically to activate transcription by the mechanisms discribed in a ?
B -Explain how two or more activitor may act synergistically to activate transcription by the mechanisms discribed in a ?
Explanation / Answer
Answer:
A. In both prokaryotes and eukaryotes, transcriptional activators and repressors are modular proteins, composed of distinct functional domains that can function without the other. The DNA binding domain binds usually to one domain of DNA, while the activation domain interacts with other proteins or another subunit of the same protein.
Activators interact with other proteins (i.e. co-activator or mediator complex) to bring in and stabilize transcription machinery, causing the intervening DNA to loop out. Mediator is the molecular bridge between activators and RNA Pol II. DNA looping mechanism brings together enhancers, transcription factors, activators, promoters and other processing factors in close proximity to facilitate the regulatory process.
Eukaryotic transcriptional activators functions by promoting the formation of RNA polymerase II preinitiation complexes at the core promoter of genes.
In yeast cells, transcriptional activation occurs when the RNA polymerase II machinery is recruited to a promoter in the form of at least two subcomplexes, TFIID and TFIIB in complex with other essential components. Individual recruitment of either complex by artificial contact with a sequence-specific, transcriptionally inactive DNA-binding protein triggers transcription activation from a wild-type core promoter bearing the appropriate binding site.
On the other hand, activation from a promoter containing a weak TATA box sequence is only observed upon recruitment of TFIID, and tethering of TFIIB on that promoter remains without effect.
B. The amount of proteins produced (transcription levels) can be adjusted in a chromatin environment by clustering binding sites into enhancers. Binding of different transcription factors (regulatory proteins) to multiple enhancer binding sites causes a superadditive effect on activating transcription, called the synergistic effect.
In the above mechanism described in (A), simultaneous recruitment of both components leads to strong synergistic activation (additive effect). These findings suggest a simple mechanism whereby two activators that contact distinct subcomplexes of the basal machinery may stimulate transcription synergistically and differentially depending on the nature of the promoter.
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