Eukaryotes can increase or decrease transcription in various ways to help regulate gene expression. A number of general transcription factors must bind to a eukaryotic promoter before RNA polymerase will bind to it and begin transcription. Other, specific transcription factors bind to regulatory DNA sequences and interact with the RNA polymerase complex to control differential gene expression.
learning outcomes
You should be able to:
Explain the various ways that transcription factors regulate gene transcription.
Describe the elements present in transcription factors that allow them to recognize and bind specific regions of DNA.
Give an example of how eukaryotic genes widely separated by location are expressed in a coordinated fashion.
What are the ways whereby transcription factors regulate the rate of gene transcription?
General transcription factors bind to the promoter and to RNA polymerase in a complex to direct RNA polymerase to the promoter to initiate transcription and locally denature DNA so that the template strand is available for base pairing during RNA synthesis. Specific transcription factors bind to specific promoters or promoters with recognition sequences. Other transcription factors bind to enhancer sequences that can be far from the actual promoter and induce DNA to bend to attract the rest of the initiation complex for transcription.
How do transcription factors recognize specific DNA sequences?
Proteins such as transcription factors fit into the DNA double helix by structural motifs, and their amino acids may form hydrogen bonds with bases on the interior of the double helix. The sequences of amino acids (proteins) and of bases (DNA) are specific so that only certain proteins bind to certain DNA sequences.
How can more than one gene be regulated at the same time in a eukaryote?
In response to a signal from the environment or within the cell, a specific transcription factor is made and/or translocated into the nucleus where it binds to a recognition sequence in DNA at the promoters of target genes. This binding attracts the initiation complex for transcription, so multiple genes are activated.
We have seen how prokaryotes and eukaryotes regulate the transcription of their genes and operons. In the next section we will see how viruses can hijack prokaryotic and eukaryotic transcription mechanisms in order to complete their life cycles.