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Genetic suppression: our beginnings with genetic engineering

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Continued experiments in molecular genetics (Part 2)
Sydney Brenner Scientist
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What we knew is that the two nonsense triplets were related to each other by base changes. So that meant they contained… that one contained an A or a U in the same place where the other contained a G or a C. We could tell that direction. And then we knew it had another U and an A, but we didn't know which way around that was. That we could tell because of failing to revert them with hydroxylamine. That meant they contained no Gs and Cs in… in the… in… they contained no Gs and Cs in… in that sequence, except for this one case where the one contained a G. Of course, we didn't know where it was but we would now determine the composition. So an experiment was done. We were in fact working on C. elegans at the time and our people were taken off that to help. The experiment took… results… needed the isolation of a few thousand R2 mutants to get the subset of amber mutants only. And these were isolated on a steady routine of a few hundred each day. They were sieved through and ultimately the two sets were mapped, complemented and identified. And it was very interesting because we had repeated occurrences of mutants. Those repeated occurrences gave us confidence that we had a… a spectrum there, that we were not just randomly choosing them. And with this spectrum we could compare the two spectra and could find certain peaks were missing in the one strain, whereas one peak was present, other peaks were present in both. That allowed us to assign that as a C, as an… a G or an A. And then by other arguments, because we had shown what amino acids in the head protein gave rise to these amber triplets, we could then say that if these amino acids are such and such and such and such, then the amber and the ochre triplets must be this. And of course we could not tell the order of this, but we could tell that they had to be either UAG, which was the amber, and UAA, which was the ochre, or it had to be AUG. And of course it was UAG because we knew what amino acids they were connected to, and those were beginning to come out. And so you could have said that had we, you know, gone on plodding in this way we might have been able to work out the whole of the code, but in fact the only survivor of the original program was this effort at determining whether the... which proved really for an immense amount of effort that there was both a U and an A in the… in the codon of the…of the nonsense codons.

South African Sydney Brenner 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: Base changes, triplets, hydroxylamine, C. elegans, R2 gene, R2 mutants, amino acid, head protein, amber mutant, codon

Duration: 3 minutes, 44 seconds

Date story recorded: April-May 1994

Date story went live: 24 January 2008