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Crystallising the nucleosome


The solenoid model
Aaron Klug Scientist
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At about the same time or in parallel with the time some people called [Dean] Hewish and [Leigh] Burgoyne in Australia, I remember Francis [Crick] telling us about this because Francis was on the... on the sidelines cheering us on, you see. Francis was there, in fact we were quite active, we used to have a... I started a group called 'What is the Magnesium?' Because that was the... you always needed magnesium to make these aggregates. But then Francis went, later he went to the States, but he was also busy with other things. But the... so the... in the end... Roger noticed that the... Hewish and Burgoyne what they found was that you sometimes had endonuclease in chromatin and the DNA was chopped into pieces of roughly 200 base pairs.

[Q] Yes.

And you can also do this is with micrococchal nuclease if you treated... treated nuclei with micrococchal nuclease, you can get fragments in 200 base pairs. And Roger was the one who proposed the nucleosome. I... I had told him first of all that there... that there wasn't 100 angstrom fibre helix, there was nothing. There was some structure of some kind repeating on 100 angstroms.

[Q] Yes.

And the... it wasn't going to be a helix but there's no indication, any other helical lines. And Roger proposed that what was happening was that the histone octamer formed a spool on which 200 base pairs were bound, which he later... which we called beads, spherical beads, much later were given the name nucleosome by Chambon in Paris, he gave the name... the French liked cartesian straight forwards when they invent names. And so the... and they published this paper and a paper in Science, two papers in Science which they proposed the nucleosome. Now, the people had seen if you take out chromatin you sort of spread it out you see little, crude little aggregates they call them new bodies, new bodies, that was there Olins and Olins. And they had no idea what the composition was or what the thing was. So they sometimes claimed to have discovered nucleosome, they didn't at all. Discovering something means you not only finding what it is and characterise it and how it's made. So that was the nucleosome and now... this was in... published in 1974, and so Roger thought, now these if you actually made such a nucleosome you put the DNA on the outside. This would be the... this would form a string of 100 angstrom; every 200 base pairs were wrapped around the nucleosome. And but that still didn't... but, I thought it was rather weak, you wouldn't get a strong 100 angstrom spacing like that, it's just a linear array.

[Q] Yes.

You need to make something more substantial. And that's when, now, you were enlisted by Roger earlier on and by han... by Marcus Noll whom Roger influenced. He was another Post Doc working in Crick's department, that this... it wasn't called, I'll call it the nucleosome but these... these nucleosomes were... so they... they chopped up... with microchoccal nuclei they chopped up chromatin into different pieces. And on sucrose gradient they found what looked like repetitive bodies, and that was the so called one, two, three, four experiment. And in the microscope you could see that the first peak looked like little spheres, the second peak, the dimer looked like two little spheres together and then three and four. And this proved... and the DNA was the 200 base pairs, 400 base pairs, 600, so it was an absolute proof of the ex... physical existence of nucleosomes. And that was the so called one, two, three, four experiment. And it still didn't explain in my view the 100 angstrom spacing, and that's why I proposed to you that there must be some higher order structure which much must be different from the linear structure. And so we did, we did the... I suggested adding magnesium, I can't remember what we did with salt... high salt as well but there was certainly magnesium, a few millimoles of magnesium. And then we could see that the... that things folded up into fibres.

[Q] Yes.

And the... now what I can't remember is we must have an H1 in our preparation fifth histone...

[Q] With and without, I think.

We did with and without, yes. But we got folding up; we got zigzag structures and folding a bit later. And so and these, and they formed the nucleosomes folded up into what we proposed as a helical structure, a super helix which would give 100 angstrom spacing as a distance between turns of the helix. We called it the 'solenoid model' because we suggest that it was tightly wound and the word super helix had already been used up; the super helix is what DNA is on the single nucleosome. So of course, the solenoid which was meant to be relatively tightly bound... and that, of course... that's been the... that was the beginning of the story.

Born in Lithuania, Aaron Klug (1926-2018) was a British chemist and biophysicist. He was awarded the Nobel Prize in Chemistry in 1982 for developments in electron microscopy and his work on complexes of nucleic acids and proteins. He studied crystallography at the University of Cape Town before moving to England, completing his doctorate in 1953 at Trinity College, Cambridge. In 1981, he was awarded the Louisa Gross Horwitz Prize from Columbia University. His long and influential career led to a knighthood in 1988. He was also elected President of the Royal Society, and served there from 1995-2000.

Listeners: Ken Holmes John Finch

Kenneth Holmes was born in London in 1934 and attended schools in Chiswick. He obtained his BA at St Johns College, Cambridge. He obtained his PhD at Birkbeck College, London working on the structure of tobacco mosaic virus with Rosalind Franklin and Aaron Klug. After a post-doc at Childrens' Hospital, Boston, where he started to work on muscle structure, he joined to the newly opened Laboratory of Molecular Biology in Cambridge where he stayed for six years. He worked with Aaron Klug on virus structure and with Hugh Huxley on muscle. He then moved to Heidelberg to open the Department of Biophysics at the Max Planck Institute for Medical Research where he remained as director until his retirement. During this time he completed the structure of tobacco mosaic virus and solved the structures of a number of protein molecules including the structure of the muscle protein actin and the actin filament. Recently he has worked on the molecular mechanism of muscle contraction. He also initiated the use of synchrotron radiation as a source for X-ray diffraction and founded the EMBL outstation at DESY Hamburg. He was elected to the Royal Society in 1981 and is a member of a number of scientific academies.

John Finch is a retired member of staff of the Medical Research Council Laboratory of Molecular Biology in Cambridge, UK. He began research as a PhD student of Rosalind Franklin's at Birkbeck College, London in 1955 studying the structure of small viruses by x-ray diffraction. He came to Cambridge as part of Aaron Klug's team in 1962 and has continued with the structural study of viruses and other nucleoproteins such as chromatin, using both x-rays and electron microscopy.

Tags: Roger Kornberg, Francis Crick, Dean Hewish, Leigh Burgoyne, Marcus Noll

Duration: 5 minutes, 45 seconds

Date story recorded: July 2005

Date story went live: 24 January 2008