In this video, we're going to talk about the first level of post-transcriptional regulation in eukaryotes, and that is alternative RNA splicing. Recall that way back in our previous lesson videos, we already covered alternative RNA splicing. If you don't remember anything about alternative RNA splicing, then make sure to go back and watch those older videos before you continue here. Eukaryotes require post-transcriptional modifications like RNA splicing, which can alter gene expression. Alternative splicing is really when different mRNA molecules are produced from the same premature RNA molecule or the same pre-mRNA. Because there are different mRNA molecules produced, that's going to lead to different proteins being made from the same gene. Different mRNA molecules will lead to different proteins being made. Recall that the spliceosome is the complex RNA-protein complex, that is going to remove introns from the pre-mRNA and splice together the exons.
If we take a look at our image down below, we have our miniature map and you can see that we're focusing on RNA processing, which is a form of post-transcriptional modifications—the splicing here that we're referring to. At the top, we have the DNA, the specific gene of interest. Within the gene, the red regions represent exons that are going to be spliced together, and the blue regions represent introns that are going to be removed. When the gene is first transcribed through transcription, a pre-mRNA molecule or a pre-mRNA transcript is formed. The pre-mRNA molecule is not going to be the fully mature mRNA. It must undergo splicing. We are zooming into the spliceosome formation, which is an assembly of a complex of RNA and protein that will come together to remove the introns, the blue regions, and splice together the red regions, the exons. That's what we're referring to here as RNA splicing.
Alternative RNA splicing is when RNA splicing can occur in multiple different ways. There are alternative pathways for RNA splicing to occur. In this image, we're focusing on just 2 different alternative pathways for RNA splicing to occur. The first RNA pathway RNA splicing pathway is over here on the left-hand side, showing you exons 1, 2, 3 all being expressed. This is the mature mRNA that's ready for translation. This is one possibility for the RNA to get spliced, and that would create this particular circular protein product upon translation. But the alternate RNA splicing pathway over here, notice, has a different mature mRNA transcript where exon 3, notice, is not available over here. It's not present. Exon 3 acted as an intron, in this alternative RNA splicing pathway. So, only exons 1, 2, and 4 are available over here. That creates a shorter polypeptide chain and that ultimately leads to a different protein. By filtering and controlling alternative RNA splicing, a specific gene product can be redirected to create a new gene product. This is a way of regulating gene expression.
This is a post-transcriptional method because the alternative RNA splicing is occurring after transcription has occurred. This here concludes our brief review and introduction of alternative RNA splicing. We'll be able to get some practice applying this as we move forward and talk about the other forms of post-transcriptional regulation. So I'll see you all in our next video.