Genetic Engineering of Viruses

by Vincent Racaniello, PhD

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    00:01 Now, the virology field was revolutionized about 30 years ago by making DNA copies of viral genomes by the recumbinant DNA technology.

    00:13 And this allows you to introduce any change into a virus that will-- that makes studying these viruses in the laboratory, making vaccines, making therapeutic products very easy. We call this an infectious DNA clone.

    00:27 Whether the virus has a DNA or an RNA genome, its genome can be made into DNA and cloned into a bacteria plasmid which can be grown in bacteria produced in high quantities.

    00:38 And then, we can introduce all sorts of changes into it.

    00:41 We can make deletion, insertion, substitution, nonsense, or missense mutations to study the virus.

    00:46 We can introduce foreign proteins to use the virus as a vector.

    00:49 For example, one of the Ebola virus vaccines that's currently being shown to be very successful in West Africa is actually a rabies-like virus with an Ebola protein coding region inserted into it.

    01:02 That was made possible by this technology.

    01:05 So, you can design any virus that you'd like, within reason, of course.

    01:09 You can reconstruct the genome from the sequence, which I'll tell you about in a moment. It's called synthetic virology.

    01:17 And because of the power of this technology, a lot of people are worried about it and so, there have been a lot of discussions over whether this is safe or not.

    01:27 Now, in this example, we're reconstructing influenza virus from a DNA copy of the RNA virus genome.

    01:34 And this, we're showing for simply one of the eight segments.

    01:37 You have to do this eight times to get an influenza virus.

    01:40 You start with the yellow molecule labeled minus RNA, that's the virus RNA genome.

    01:46 You make a double-stranded DNA copy of it, you put it in a plasmid and that plasmid when introduced into cells, will produce both negative-stranded viral RNA as well as plus-stranded mRNA to make proteins.

    01:58 So, you put eight of these plasmids into cells, one coding for each of the viral segments and outcomes infectious virus.

    02:07 We call this transfection. We introduce a DNA into cells and outcomes virus.

    02:13 Let me tell you an interesting news of this technology.

    02:16 Back in 1918, there was a huge and very serious outbreak of influenza virus.

    02:23 It's often called Spanish flu, although that's not where it originated.

    02:27 This outbreak killed millions of people globally, coincided with World War I, so troop movements probably had a lot to do with its spread.

    02:38 But we didn't have this virus isolated from this outbreak.

    02:41 We didn't isolate influenza virus until 1933.

    02:45 So, in the 1990s, investigators determined the sequence of this virus because it had never been isolated.

    02:56 They determined the sequence from material that had been obtained from people who died and were frozen in Alaska.

    03:06 They opened the grave, they took biopsies of the lungs.

    03:09 These people were known to die--have died from influenza virus, and then they extracted enough material to determine the genome sequence.

    03:17 They also got more sequence from pathology slides that had been prepared from army recruits who had died of the infection.

    03:24 Their lungs had been sectioned and preserved and stored, and we could recover a little bit of sequence from that as well.

    03:30 So, the sequence of all eight segments was determined.

    03:33 It was built into DNA and the virus was recovered.

    03:36 So, we reconstructed the 1918 virus when we never had it before.

    03:41 We reconstructed it from the sequence.

    03:43 So, this can be done with just about any virus.

    03:45 And people have been studying this virus and we've learned a lot about it.

    03:48 We've learned many important things and of course, all of these studies are done under high containment because if this virus got out, it could likely be very dangerous.

    About the Lecture

    The lecture Genetic Engineering of Viruses by Vincent Racaniello, PhD is from the course Viruses.

    Author of lecture Genetic Engineering of Viruses

     Vincent Racaniello, PhD

    Vincent Racaniello, PhD

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