Examples of Transcription Regulation in Eukaryotes

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  • 1:34 DNA Regulatory Regions
  • 4:11 DNA Methylation and…
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Lesson Transcript
Instructor: Kristin Klucevsek

Kristin has taught college Biology courses and has her doctorate in Biology.

Transcription is more complicated than just turning a gene 'on' or 'off' like a light switch. In this lesson, you'll learn how eukaryotic transcription is regulated through the use of DNA regulatory regions, DNA methylation, and chromatin modification.

Eukaryotic Transcription Regulation

Remember that transcription is the process that creates RNA from DNA using RNA polymerase in all living organisms. In eukaryotic cells, the genome is housed in the nucleus. This creates a separate space for transcription, allowing for a more complicated process than in prokaryotic cells, or cells without a nucleus.

Transcription, otherwise known as gene expression, is one of my favorite cellular processes. All cells within your body have the same DNA sequence, and yet you have so many different types of cells that they all look different and act different from each other, like skin cells, heart cells, liver cells, etc. So, how does that happen? It all comes down to which genes are expressed, or transcribed, and to what level they are expressed. You see, when it comes to transcription, it's not always as simple as whether the gene is on or off, like a light switch. A gene that is on, but only at low or basic levels of transcription, is known as basal transcription. However, a gene can be transcribed at higher rates when necessary. Think of it like a music dial. 'Off' is off, but 'on' can be a little background music or full-on party mode.

Now while we might regulate the music with a simple turn of the dial, regulating transcription is a much more complicated task, and there are several ways to do this. This is especially true in eukaryotic cells. In this lesson, we'll delve into a few of the mechanisms used to regulate levels of eukaryotic transcription, including different DNA regulatory regions, DNA methylation, and chromatin modifications.

DNA Regulatory Regions

Transcription can be regulated by changing what transcription factors, or those proteins that control transcription levels, are bound to different parts of the DNA. Think of it this way: the dial stays the same, but the level that the music is blaring will depend on who's controlling the tunes.

To understand this best, we need to acquaint ourselves with the basic structure of a gene. Remember that only 2% of the human genome is protein-coding DNA. Much of the remaining 98% of DNA does a lot of cool things, including transcriptional control. We'll use a line below to represent one gene on a chromosome. For the sake of this lesson, let's keep the gene rather simple, with a 5' and a 3' end, using the blue region to represent DNA that is transcribed. However, keep in mind that this blue gene represents many parts, such as the 5' UTR, introns, exons, and 3' UTR. Now, in addition to this region, there are multiple DNA regulatory regions. These are segments of DNA where transcription factors can bind to control transcription - to turn that dial up and down.

This line is representative of one gene on a chromosome.
DNA representation

Next to the gene is the promoter. You may know the promoter already as the region where RNA polymerase binds to initiate transcription. Not all promoters have the same DNA sequence, even though RNA polymerase binds at all promoters. However, some eukaryotic promoters contain a specialized promoter sequence known as the TATA box. A specific transcription factor, appropriately called the TATA-binding protein, binds here to help start transcription. Other promoters without a TATA box could use different transcription factors for the same purpose. Therefore, parts of all promoters can also be DNA regulatory regions, even if they don't contain a TATA box.

Another DNA regulatory region is known as the enhancer. This is a region of DNA where transcription factors can bind to greatly increase gene transcription. Enhancers do exactly what they sound like - they enhance transcription, beyond those basal levels. Sure, transcription could take place without them, but with them, it's so… enhanced! Right? So, not all genes have to have enhancers, and not all enhancers are the same DNA sequence. But a really cool thing about enhancers is that they can be located really far from the gene they influence.

While there are other DNA regulatory regions for controlling transcription, the promoter and enhancer are binding sites for a variety of transcription factors, and therefore, they're really influential to eukaryotic gene expression. In addition, while many transcription factors are responsible for turning genes on, there are also many transcription factors that would turn genes off, or dial down transcription levels.

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