Transposable Elements

by Georgina Cornwall, PhD

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    00:00 RNA seems to have a big role in regulating gene expression and so do many of these non-coding regions. We are going to take a deeper look into transposable elements or transpose on some jumping genes because I think they are particularly interesting. Very very lively area of research at the moment.

    00:23 If we look at this Pi chart, you can see that there are a lot of different sorts of transposons.

    00:30 Some of them are dead. We will look at those in a little more detail. We have some long terminal repeats those, towards the ends of chromosomes. We have some short interspersed elements.

    00:43 We have got more and more acronyms here, science and lines and we have lines long interspersed elements and then we have the rest of the DNA. Over 45 percent of our genome is made up of transposable elements or jumping genes. So tell me they don't have some sort of role and we are finding out that they really do. The rest of the genome with non-coding and coding DNA that is 55 percent. So a lot of our genome has to do with these transposable elements.

    01:19 Let us take a little bit of a closer look at what some of them do. LINES are long interspersed elements. They are long. They are about 6000 base pairs. They can price about 21 percent of the human genome. That is kind of a lot. They have their own machinery that allows them to transpose themselves. Basically, they can cut themselves out of the genome and they can copy themselves and insert themselves into another genome. They contain genes that code for proteins that allow them to do all of these themselves. It is pretty cool.

    01:57 That is when I first started realizing they must be up to something. They have a purpose if they have all those types of machinery. We might see retrotransposons. A lot of transposons are retrotransposons. That don't mean they are really old, but it means more that they are able to make a copy of themselves. We have transcription. We make mRNA and that mRNA if they have a gene for reversed transcriptase can then be reversed transcribed back into DNA so that they can put that transposable element somewhere else in the genome. Literally these genes do jump around all over the genome. Pretty exciting I think.

    02:41 Inside of LINEs sometimes we find SINES, short interspersed elements. They are shorter and they utilized the machinery of the LINEs, the long interspersed elements. They are often embedded inside long interspersed elements to use their machinery.

    03:01 Again LINE involved genes that code for the machinery or the enzymes or proteins involved in transcription and translation of themselves and the endonucleases that might cut DNA and allow them to pop back into a sequence somewhere else. Often signs are seen to interrupt genes.

    03:24 Let us say theoretically, we didn't want this particular gene expressed a sign may come jumping in there and jump into that gene and stop it from making any sense. It is interrupting the genes so when that gene or that gene would not be transcribed into a successful mRNA or translated into a successful protein. SINEs embedded in LINEs often involved in interrupting in other genes. Then we have long terminal repeats. Long terminal repeats also code for the round reverse transcriptase so that they can transcribe themselves from messenger RNA making a DNA copy that they can stuff back into the genome some where else.

    04:12 Very exciting stuff with all of these different transposable elements because they all seem to be having some sort of impact on gene expression and moving junks of DNA around, again a huge area of research presently. So the final piece are these dead transposons. It seems like dead transposons are transposons that no longer have the machinery associated with them to transpose themselves. We really don't have a clear understanding of what that transposons do or if they are simply dead or do they have some other kind of role. The long and the short of it is, there is a lot of material that is not coding DNA that probably impacts how DNA is actually expressed.

    05:02 That could account for why we have much less coding gene than we have thought we might have when we were initially sequencing the genome. Our complexity could come around because of all of these different pieces of DNA particularly transposons and RNA coding sections that might regulate gene expression.

    About the Lecture

    The lecture Transposable Elements by Georgina Cornwall, PhD is from the course Genomics.

    Included Quiz Questions

    1. Introns
    2. Structural DNA
    3. Transposable elements
    4. Pseudogenes
    5. Tandem clusters
    1. LINES and SINES contain machinery to transpose themselves
    2. Transposable elements make up 45% of the human genome.
    3. They likely have little effect on gene expression.
    1. Transposon ----- Highly conserved region of non-coding DNA to provide structural support to the centromeres.
    2. Retrotransposon ---- Transposon transcribed to RNA, and then that RNA gets reverse transcribed to produce its DNA copy to insert at the new position in the genome.
    3. LTRs ----- Identical sequences of DNA that repeat hundreds of times and found at either end of retrotransposons.
    4. LINEs ----- A family of transposons having an information of reverse transcriptase enzyme for its transposition.
    5. SINEs -----50-500 bp long non-autonomous and non-coding transposable elements.

    Author of lecture Transposable Elements

     Georgina Cornwall, PhD

    Georgina Cornwall, PhD

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