What are some of the steps in eukaryotic transcriptional control? (a) A transcri

Question

What are some of the steps in eukaryotic transcriptional control?

(a) A transcriptional repressor recruits nucleosome remodeling proteins that alter nucleosome positioning, modification, and composition. This allows for the formation of a closed chromatin complex, and binding of general transcription factors and RNA polymerase II. Histone cores remain on the gene as transcript elongation occurs.

(b) A transcriptional repressor recruits general transcription factors and RNA polymerase II without affecting nucleosome positioning.

(c) A transcriptional activator recruits nucleosome remodeling proteins that alter nucleosome positioning, modification and composition. This allows for the formation of an open chromatin complex, and binding of general transcription factors and RNA polymerase II. Finally as transcription elongation occurs, histone cores are evicted from the DNA to allow the RNA polymerase to transcribe the gene.

(d) A transcriptional activator recruits general transcription factors and RNA polymerase II. Finally as transcription elongation occurs, histone cores remain with the DNA.

Explanation / Answer

Initiation of DNA transcription in eukaryotes by RNA polymerase II is activated by promoter and enhancer elements. Eukaryotic transcriptional activators are modular proteins that are typically composed of a sequence-specific DNA binding domain and an activating region /domain. The activators interact through their activating regions with components of the RNA polymerase II transcriptional apparatus that bind promoters. It has been shown that some activators can also interact with factors that modify or remodel nucleosomes (chromatin). The activator interaction with one or more transcription factors attracts the transcription complex near the site of gene promoter, and facilitate the binding to the promoter (recruitment). Formation of this protein–DNA complex at the promoter provides the signal for the RNA polymerase to initiate and elongate transcription. The DNA binding and activation domains of different factors can frequently be interchanged using recombinant DNA techniques. The transcriptional activator proteins can cause complete unfolding, and probably dissociation, of histones from promoter regions. The transcriptional activators, can also through interaction with ‘specialized’ targets, induce conformational change that activates the RNA polymerase for transcription , initiation and elongation.Studies have shown that histone-DNA interactions are more dynamic, maintaining an equilibrium of histone eviction and deposition.

Based on these conclusions it can be infered that step (C) can happen during the eukaryotic transcriptional control.

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