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  • mRNA, and eventually proteins, are produced when and where they are needed in an organism.

  • Some genes, such as those for housekeeping proteins in processes like glycolosis,

  • are expressed all of the time.

  • These genes undergo what is known as constitutive transcription.

  • Other proteins are only produced at specific times in certain cells.

  • In these cells, genes undergo a process

  • called regulated transcription.

  • Transcription is regulated by proteins called transcription factors.

  • These factors are proteins that are produced in the cytoplasm

  • and eventually migrate into the nucleus

  • where they interact with DNA and activate transcription.

  • These transcription factors only interact with specific genes,

  • those genes whose transcription they control.

  • Most eukaryotic species have over 1000 transcription factors.

  • Regulated transcription begins when a signal is received by the cell.

  • This signal, often a protein,

  • begins a signal transduction cascade

  • that lets the cell know certain proteins are now needed.

  • The most common activation event for a protein in a signal pathway

  • is the addition of a phosphate group.

  • That activated protein in turn interacts with another protein.

  • This interaction leads to the phosphorylation of the next protein in the pathway.

  • There is often a series of proteins that are activated by phosphorylation.

  • At the end of this cascade,

  • the final protein will be activated and then enter the nucleus.

  • It must make this journey because transcription only occurs inside the nucleus.

  • After entering through a nuclear pore,

  • the protein interacts with the specific transcription factor responsible for activating

  • mRNA production.

  • As with the earlier proteins,

  • the transcription factor is modified through phosphorylation.

  • The activated transcription factor will next bind to an enhancer region.

  • The enhancer is a region of DNA

  • upstream of the transcription start site

  • that binds a transcription factor.

  • The transcription factor then binds to the DNA

  • and moves to interact with the rest of the transcription protein complex,

  • located at the transcription start site.

  • When the formation of this complex is complete,

  • transcription of the gene will begin.

  • It is this sequence of events

  • that ensures genes required for a specific tissue

  • or only at a specific time

  • are expressed appropriately.

mRNA, and eventually proteins, are produced when and where they are needed in an organism.

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B2 中上級

制御された転写 (Regulated Transcription)

  • 33 5
    Szu-Pei Wu に公開 2021 年 01 月 14 日
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