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DNA and RNA synthesis


Genetics of the rII and the gene protein problem
Sydney Brenner Scientist
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Well, during this period we were doing many things simultaneously, one of… simultaneously. One of the things was… was the genetics of the R2; the other was trying to work on the gene protein problem. Now, the gene protein problem went ahead, and one of the things we discovered is that the protein that was very easy to purify in very large amounts was the head protein of the bacteriophage. The amazing thing is that when one studied what happened after infection with this bacteriophage, this single protein accounted for 70% of all the protein synthesis of the cell. Now, what you have to understand is that at that time it was believed that the ribosomes carried the information from the gene to the protein. That is the RNA of the ribosomes was the material that was so to speak the information intermediate. But already a lot of experiments seemed to make that very questionable. One of the experiments that created some concern was a whole set of analyses of the RNA of bacteria and of the DNA bacteria and it had been known for some time and strongly reinforced during this period that whereas the base composition – that is the amount of G + C to A + T – varied in bacteria over an enormous range. That is, they were bacteria whose DNA was 3/4 (G + C), down to bacteria whose DNA was 3/4 (A + T). That... that paradox was accompanied by a complete invariance of the RNA. The RNA seemed to have about the same base composition in all the bacteria. This gave rise to a lot of problems because, as you can see, if the DNA is supposed to carry the message, why did it vary so much? You would have thought that the language of the code was pretty invariant. Now there were two kinds of theories to get out of this. One was… and it's very… it echoes things we think about today, so one was the DNA of bacteria was made up of two kinds. One was invariant and looked like the DNA... the composition of the RNA; and the other was variable, in fact it was just a lot of junk. And again there were 'don't worry' theories as to how to do this. Now the Junk Hypothesis had to be discarded when Doty and Sueoka showed that the dispersion of the DNA of this base composition was homogeneous. That is it was finely dispersed. They did this by measuring the density of the DNA and it's known that the density of G + C is different from the density of A + T. If the Junk Theory was correct you would have expected that DNAs from different bacteria would split into two fractions. One which corresponded to the bulk analysis, and then one smaller fraction which would have been the genes, and what they found is that the DNA base composition of the whole went down to rather small regions of DNA homogeneously. So that means that it was there, and of course this gave rise to the concept that in fact the code may be degenerate in some form. In fact Sinsheimer did… did in fact make a suggestion of this, that essentially the code was… it would have to be a pyrimidine purine code and not depend on which purine or this, so he did make a suggestion of a Binary Code. That of course is wrong, but I mean that is what we had to face. But what we could not explain is why is the base composition of the ribosomes invariant.

South African Sydney Brenner (1927-2019) was awarded the Nobel Prize in Physiology or Medicine in 2002. His joint discovery of messenger RNA, and, in more recent years, his development of gene cloning, sequencing and manipulation techniques along with his work for the Human Genome Project have led to his standing as a pioneer in the field of genetics and molecular biology.

Listeners: Lewis Wolpert

Lewis Wolpert is Professor of Biology as Applied to Medicine in the Department of Anatomy and Developmental Biology of University College, London. His research interests are in the mechanisms involved in the development of the embryo. He was originally trained as a civil engineer in South Africa but changed to research in cell biology at King's College, London in 1955. He was made a Fellow of the Royal Society in 1980 and awarded the CBE in 1990. He was made a Fellow of the Royal Society of Literature in 1999. He has presented science on both radio and TV and for five years was Chairman of the Committee for the Public Understanding of Science.



Listen to Lewis Wolpert at Web of Stories



Tags: Paul Doty, Noburo Sueoka, Robert Sinsheimer

Duration: 5 minutes, 2 seconds

Date story recorded: April-May 1994

Date story went live: 24 January 2008