transcription factor

Examples of transcription factor in the following topics:

• The Promoter and the Transcription Machinery

  • The purpose of the promoter is to bind transcription factors that control the initiation of transcription.
  • 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.
  • The region that a particular transcription factor binds to is called the transcription factor binding site.
  • Transcription factors recognize the promoter.

• Cancer and Transcriptional Control

  • Mutations that activate transcription factors, such as increased phosphorylation, can increase the binding of a transcription factor to its binding site in a promoter.
  • Alternatively, a mutation in the DNA of a promoter or enhancer region can increase the binding ability of a transcription factor.
  • Identifying how a transcription factor binds, or a pathway that activates where a gene can be turned off, has led to new drugs and new ways to treat cancer.
  • This can lead to increased phosphorylation of key transcription factors that increase transcription.
  • The EGFR pathway activates many protein kinases that, in turn, activate many transcription factors that control genes involved in cell growth.

• 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).
  • One transcription factor, Transcription Factor II H (TFIIH), is involved in separating opposing strands of double-stranded DNA to provide the RNA Polymerase access to a single-stranded DNA template.
  • Transcription factors recognize the promoter, RNA polymerase II then binds and forms the transcription initiation complex.

• Transcriptional Enhancers and Repressors

  • Enhancer regions are binding sequences, or sites, for transcription factors.
  • This shape change allows the interaction between the activators bound to the enhancers and the transcription factors bound to the promoter region and the RNA polymerase to occur.
  • Like the transcriptional activators, repressors respond to external stimuli to prevent the binding of activating transcription factors.
  • A corepressor is a protein that decreases gene expression by binding to a transcription factor that contains a DNA-binding domain.
  • Activators bound to the distal control elements interact with mediator proteins and transcription factors.

• Mechanics of Cellular Differentation

  • Cellular differentiation, a necessary process in development and maintenance of multicellularity, is regulated by transcription factors.
  • The primary mechanism by which genes are turned "on" or "off" is through transcription factors.
  • A transcription factor is one of a class of proteins that bind to specific genes on the DNA molecule and either promote or inhibit their transcription .
  • Through the action of these transcription factors, cells specialize into one of hundreds of different cell types in the human body.
  • Transcription factors are proteins that affect the binding of RNA polymerase to a particular gene on the DNA molecule.

• 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).
  • Therefore, changes in histone acetylation (epigenetic modification that leads to gene silencing), activation of transcription factors by phosphorylation, increased RNA stability, increased translational control, and protein modification can all be detected at some point in various cancer cells.
  • The p53 protein itself functions as a transcription factor.
  • It can bind to sites in the promoters of genes to initiate transcription.
  • Myc is a transcription factor that is aberrantly activated in Burkett's Lymphoma, a cancer of the lymph system.

• Epigenetic Control: Regulating Access to Genes within the Chromosome

  • If DNA encoding a specific gene is to be transcribed into RNA, the nucleosomes surrounding that region of DNA can slide down the DNA to open that specific chromosomal region and allow for the transcriptional machinery (RNA polymerase) to initiate transcription .
  • This opens the chromosomal region to allow access for RNA polymerase and other proteins, called transcription factors, to bind to the promoter region, located just upstream of the gene, and initiate transcription.
  • In this closed configuration, the RNA polymerase and transcription factors do not have access to the DNA and transcription cannot occur.
  • When nucleosomes are spaced closely together (top), transcription factors cannot bind and gene expression is turned off.
  • Transcription factors can bind, allowing gene expression to occur.

• Prokaryotic versus Eukaryotic Gene Expression

  • When the resulting protein is no longer needed, transcription stops.
  • When more protein is required, more transcription occurs.
  • 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.
  • Regulation may occur when the DNA is uncoiled and loosened from nucleosomes to bind transcription factors (epigenetics), when the RNA is transcribed (transcriptional level), when the RNA is processed and exported to the cytoplasm after it is transcribed (post-transcriptional level), when the RNA is translated into protein (translational level), or after the protein has been made (post-translational level).
  • Prokaryotic transcription and translation occur simultaneously in the cytoplasm, and regulation occurs at the transcriptional level.

• Cell Signaling and Gene Expression

  • When the resulting protein is no longer needed, transcription stops.
  • When more protein is required, more transcription occurs.
  • 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 in the cytoplasm.
  • Regulation may occur when the DNA is uncoiled and loosened from nucleosomes to bind transcription factors (epigenetic level); when the RNA is transcribed (transcriptional level); when the RNA is processed and exported to the cytoplasm after it is transcribed (post-transcriptional level); when the RNA is translated into protein (translational level); or after the protein has been made (post-translational level).
  • Prokaryotic transcription and translation occur simultaneously in the cytoplasm; regulation occurs at the transcriptional level.

• Elongation and Termination in Eukaryotes

  • Following the formation of the pre-initiation complex, the polymerase is released from the other transcription factors, and elongation is allowed to proceed with the polymerase synthesizing RNA in the 5' to 3' direction.
  • This process continues until transcription termination occurs.
  • The termination of transcription is different for the three different eukaryotic RNA polymerases.
  • The ribosomal rRNA genes transcribed by RNA Polymerase I contain a specific sequence of basepairs (11 bp long in humans; 18 bp in mice) that is recognized by a termination protein called TTF-1 (Transcription Termination Factor for RNA Polymerase I.)
  • RNA Polymerase II has no specific signals that terminate its transcription.