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Self-splicing intron RNAs: ribozymes, parasites and agents of genomic change
A selection of talks on Cell Biology
Gene structure, expression and regulation: DNA structure and replication
- Dr. Carole Sargent
- University of Cambridge, UK
Preclinical translation of mesenchymal stem cell therapies
- Dr. Peter Childs
- University of Strathclyde, UK
In this talk, we'll be going over the characteristics of the self-splicing intron RNAs, which include the group one and the group two introns, and hopefully by the end, you'll see what kinds of properties they have as ribozymes, as folded RNAs, and see what kind of context they have biologically as parasites and agents of genomic change.
The latter part of the talk will include experiments that were done primarily in my own lab, and your narrator is indicated by the yellow arrow in this picture. But it's important to say that much of the talk will also be about group one introns and I worked on those as a postdoc in Tom Cech's lab.
Before we review the specifics of group one and group two introns, it's important to review what an intron actually is. When a gene is actually transcribed into RNA, there are regions of the RNA that contain information that is not supposed to make its way into the functional product. And these intervening regions of sequence, which I've shown here in blue are called introns. The functional regions of the RNA are called exons, shown here as exon 1 and exon 2. Through the process of splicing, introns are removed and discarded and the exons are stitched together again to create a functional gene. It's important to point out that a typical gene, encoding one of your proteins, i.e. a eukaryotic gene, is highly complex and requires the splicing of many exons and removal of many introns. So splicing is a fundamental process in gene expression, particularly in eukaryotes.
So what happens with these discarded introns? Well, sometimes they are indeed junk that requires recycling, but sometimes introns are innately useful, and they serve other functions in a cell. They can encode proteins, they can encode small regulatory RNAs such as micro RNAs or small RNAs involved in RNAi. The splicing of introns and the sequence of splicing can be contribution to gene expression, but more pertinent to today's talk is that some introns are genomic parasites. Group one and group two introns are mobile genetic elements, that can hop from place to place within a genome or hop from genome to genome, thereby affecting evolution. There are four major categories of intron and each of