Renato Dulbecco - Understanding polyoma DNA (20/61) скачать в хорошем качестве

Renato Dulbecco - Understanding polyoma DNA (20/61)

To listen to more of Renato Dulbecco’s stories, go to the playlist:    • Renato Dulbecco (Biologist)   The Italian biologist Renato Dulbecco (1914-2012) had early success isolating a mutant of the polio virus which was used to create a life-saving vaccine. Later in his career, he initiated the Human Genome Project and was jointly awarded the Nobel Prize in Physiology or Medicine in 1975 for furthering our understanding of cancer caused by viruses. [Listener: Paola De Paoli Marchetti; date recorded: 2005] TRANSCRIPT: So, coming back to what I started to talk about before, that is, the polyoma virus and I was saying that its genome was made of DNA and that therefore it was right for me, in order to carry out all the work that was needed to understand how this DNA worked. And one of the things that I did straight away was to... I don't know if I really did it as a specific task or whether it came about while I was working with the virus, with viral DNA that I saw that this viral DNA was present in two forms and this could be seen particularly... to isolate the DNA, what is generally done is to put this virus that has DNA in it and protein outside, to put it in a substance that – a type of soap – that breaks the protein in such a way as to separate the proteins and the DNA, and then everything is placed in a centrifugal tube, where there is a thicker gradient at the bottom, less dense on the surface, or simply a gradient to maintain localisation. This is the aim, because this DNA needs to be sedimented in the test-tube, but you need to be certain that while it sedimentates, it remains where it is, then, because otherwise you cannot take it out of the tube, it would no longer be there. Doing this, generally, with this type of virus there is only a single band of this viral DNA, however here there were two and this amazed me. Then I saw, looking at the literature, that a similar observation had been made with the papyloma virus, which is also DNA, and this was interpreted by the fact that there were virus particles which had one DNA length and others that had two lengths, therefore those which had one length moved more quickly... no, actually it's the other way round, those that had two lengths moved more quickly and those that had one stayed behind more. So, to resolve this problem, we carried out what we call a column. A column means – you take a glass tube into which you put a substance which DNA tends to attack, but not permanently, so that if it makes this DNA go down through this column, every so often it attacks and so slows and then it attacks again and then slows down, so that if it is longer it has more possibility of attacking, if it is shorter, there is less possibility. Therefore, if one is of double length, it would stay more at the top, it would be more slowed down than the one with the single length. We did this with the polyoma DNA and we saw, instead that they came together, so, therefore, it is not a question of length, it's a question of structure and then: what is the structure? There are two possibilities: that of using to see and using the effect of an enzyme that cuts the DNA and the other was to observe these DNA molecules under an electronic microscope, because under a normal microscope you can't see, they are too small, but under an electronic microscope you can see properly. I started with enzymes, with DNase, as the enzyme that cuts DNA is called and, using this in very small doses, you could obtain a single cut per molecule and when I did this, I saw that the molecule that was the quickest, slowed down, so the cut caused a slowing down and there a possibility that seemed easy was that the DNase was cutting this molecule in a way that it was not cutting it into two pieces, but it always stayed in one piece, because it was circular. With the cut of a circle, a longer linear molecule was obtained and then this longer molecule... not longer, the same length, but a different shape I thought would have slowed down, given its shape. Then the important thing was to carry out the test under the electronic microscope; however this didn't work, very strange indeed. There in Caltech, we didn't have an electronic microscope, they had one in the Chemistry department and I needed to check it with them and I tried loads of times to do this. I don't know, I think that there was some problem or other with the person in charge. Finally, I gave up and I published works saying that there were two shapes, one round and one not round, linear. Afterwards it emerged that this wasn't true and the shape that I... yes, was circular, but there were two circular shapes, a circular shape that... [...] Read the rest of the transcript at https://www.webofstories.com/play/ren...