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| Gene Control |
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Genes are not constantly being transcribed in order to make proteins. Rather, genes can be turned on or off in a cell. If they are turned on, the rate of transcription, and therefore protein production, can vary.
There are a number of factors that initiate gene transcription, and regulate the rate at which initiation occurs.
Upstream of the coding sequence is a promoter region of DNA, to which a protein called a transcription factor binds.
The promoter contains a region called the TATA box, a short sequence of T-A and A-T base pairs recognized by the general transcription factor TFIID. The TATA box is usually 25 base pairs upstream from the transcription start site.
In eukaryotic organisms, a general transcription factor must bind to a promoter before the RNA polymerase enzyme can initiate transcription.
The RNA polymerase then transcribes the gene from genomic DNA (on a chromosome in the nucleus), to mRNA (which moves through nuclear pores into the cytoplasm, where it can be translated into protein). RNA polymerase ceases transcription at the stop codon, which is usually TAA, TAG, or TGA.
In addition to transcription factors, there are thousands of different regulatory proteins. Some regulatory proteins stimulate gene transcription (e.g., gene activator proteins), while others repress it (e.g., gene repressor proteins).
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Reference: Alberts, B., Bray, D., Lewis, J., Raff, M., Roberts, K., Watson, J. 1994. Control of Gene Expression. Chapter 9 in Molecular Biology of the Cell. 3rd ed. New York: Garland Publishing.
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| Try This... |
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- Search PubMed for "gene control" in the Title Word field.
- Diplay one of the records in Abstract format, and follow the Books link.
- PubMed will display the same record, but will highlight the terms and concepts that are explained in online books such as Molecular Biology of the Cell. 3rd ed, by B. Alberts, et al. (1994).
- Follow the link for "gene control" to see a list of pertinent textbook sections.
- From the list of textbook sections, choose one that talks about control of gene expression.
- Note that you might see the term "regulation," or "regulatory" rather than "control." For example, the subsection "A Eucaryotic Gene Control Region Consists of a Promoter Plus Regulatory DNA Sequences" is part of Chapter 9: Control of Gene Expression, in the section on "How Genetic Switches Work." If you find that subsection, follow the the link for it.
- Follow the link for Figure 9-34 to see a nice diagram of "the gene control region of a typical eukaryotic gene."
- Go back to the previous page. The orange sidebar contains an outline of the chapter, leading to additional information on the Control of Gene Expression.
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