transcription

(noun)

the synthesis of RNA under the direction of DNA

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Examples of transcription in the following topics:

  • The Promoter and the Transcription Machinery

    • When transcription factors bind to the promoter region, RNA polymerase is placed in an orientation that allows transcription to begin.
    • The purpose of the promoter is to bind transcription factors that control the initiation of transcription.
    • RNA polymerase binds to the transcription initiation complex, allowing transcription to occur.
    • To initiate transcription, a transcription factor (TFIID) is the first to bind to the TATA box.
    • In addition to the general transcription factors, other transcription factors can bind to the promoter to regulate gene transcription.
  • Cancer and Transcriptional Control

    • Alterations in cells that give rise to cancer can affect the transcriptional control of gene expression.
    • Mutations that activate transcription factors, such as increased phosphorylation, can increase the binding of a transcription factor to its binding site in a promoter.
    • This could lead to increased transcriptional activation of that gene that results in modified cell growth.
    • This can lead to increased phosphorylation of key transcription factors that increase transcription.
    • Transcription factors, especially some that are proto-oncogenes or tumor suppressors, help regulate the cell cycle; however, when regulation gives rise to cancer cells, then transcriptional control of gene expression is affected.
  • Transcriptional Enhancers and Repressors

    • Enhancers increase the rate of transcription of genes, while repressors decrease the rate of transcription.
    • Enhancer regions are binding sequences, or sites, for transcription factors.
    • Transcriptional repressors can bind to promoter or enhancer regions and block transcription.
    • Like the transcriptional activators, repressors respond to external stimuli to prevent the binding of activating transcription factors.
    • An enhancer is a DNA sequence that promotes transcription.
  • Prokaryotic versus Eukaryotic Gene Expression

    • When the resulting protein is no longer needed, transcription stops.
    • When more protein is required, more transcription occurs.
    • Therefore, in prokaryotic cells, the control of gene expression is mostly at the transcriptional level.
    • The processes of transcription and translation are physically separated by the nuclear membrane; transcription occurs only within the nucleus, and translation occurs only outside the nucleus within the cytoplasm.
    • Prokaryotic transcription and translation occur simultaneously in the cytoplasm, and regulation occurs at the transcriptional level.
  • Initiation of Transcription in Eukaryotes

    • Initiation is the first step of eukaryotic transcription and requires RNAP and several transcription factors to proceed.
    • The completed assembly of transcription factors and RNA polymerase bind to the promoter, forming a transcription pre-initiation complex (PIC).
    • The TATA box, as a core promoter element, is the binding site for a transcription factor known as TATA-binding protein (TBP), which is itself a subunit of another transcription factor: Transcription Factor II D (TFIID).
    • Activator proteins increase the transcription rate, and repressor proteins decrease the transcription rate.
    • Transcription factors recognize the promoter, RNA polymerase II then binds and forms the transcription initiation complex.
  • Cancer and Post-Transcriptional Control

    • Modifications, such as the overexpression of miRNAs, in the post-transcriptional control of a gene can result in cancer.
    • Post-transcriptional regulation is the control of gene expression at the RNA level; therefore, between the transcription and the translation of the gene.
    • After being produced, the stability and distribution of the different transcripts is regulated (post-transcriptional regulation) by means of RNA-binding proteins (RBP) that control the various steps and rates of the transcripts: events such as alternative splicing, nuclear degradation (exosome), processing, nuclear export (three alternative pathways), sequestration in DCP2-bodies for storage or degradation, and, ultimately, translation.
    • Changes in the post-transcriptional control of a gene can result in cancer.
  • Initiation of Transcription in Prokaryotes

    • These subunits assemble each time a gene is transcribed; they disassemble once transcription is complete.
    • The fifth subunit, σ, is involved only in transcription initiation.
    • A promoter is a DNA sequence onto which the transcription machinery binds and initiates transcription .
    • The transcription initiation phase ends with the production of abortive transcripts, which are polymers of approximately 10 nucleotides that are made and released.
    • The σ subunit dissociates from the polymerase after transcription has been initiated.
  • Elongation and Termination in Prokaryotes

    • The transcription elongation phase begins with the release of the σ subunit from the polymerase.
    • The interaction with rho releases the mRNA from the transcription bubble.
    • The complementary U–A region of the mRNA transcript forms only a weak interaction with the template DNA.
    • Upon termination, the process of transcription is complete.
    • In contrast, the presence of a nucleus in eukaryotic cells prevents simultaneous transcription and translation.
  • Altered Gene Expression in Cancer

    • This can be the result of gene mutation or changes in gene regulation (epigenetic, transcription, post-transcription, translation, or post-translation).
    • The p53 protein itself functions as a transcription factor.
    • It can bind to sites in the promoters of genes to initiate transcription.
    • Therefore, the mutation of p53 in cancer will dramatically alter the transcriptional activity of its target genes.
    • Myc is a transcription factor that is aberrantly activated in Burkett's Lymphoma, a cancer of the lymph system.
  • Elongation and Termination in Eukaryotes

    • RNA Polymerase II will continue to elongate the newly-synthesized RNA until transcription terminates.
    • As a result, RNA strand synthesis occurs in a transcription bubble of about 25 unwound DNA basebairs.
    • This process continues until transcription termination occurs.
    • The termination of transcription is different for the three different eukaryotic RNA polymerases.
    • RNA Polymerase II has no specific signals that terminate its transcription.
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