Polymerase Chain Reaction
Making DNA accessible
When it first happened on California 128 between Cloverdale and Booneville sometime before midnight on a Friday in April 1983, it was a possible solution to a hypothetical problem that might have occurred in a proposed method for determining an unknown base pair adjacent to a known sequence, not unlike sequencing SNPs today, a method that when applied to unamplified human DNA, and that's the only kind there was then, would have absolutely not worked. The method, proposed by my chemist self unaware of the practical impact of three times ten to the ninth did not take into account the immense complexity of the human genome or in fact the other very real problem that PCR was going to so elegantly solve.
At the time there was never enough DNA in any experiment, i.e., it was always limiting, and whatever human DNA there was in an experiment was hopelessly contaminated with itself. It all looked alike from a distance and whatever part of it you might be interested in, or somebody might be paying you to study, or more urgently the part you were interested in because you were trying to cure yourself of cancer, as one of my colleagues was, whatever part you chose to study, it always resided in the same tube as a million other parts. When you isolated human DNA, every microgram contained three hundred and thirty thousand copies of every sequence in the genome, but each copy in the process of isolation would be broken off into its own little piece with its own molecular weight. There was no logic in the process.
Unless you employed the bacterial enzymes called restriction endonucleases. With these specialized little DNA scissors, you could induce some order in the chaos; you could by very specifically cutting your sequence once on each end, assure that at least most (nothing is perfect in chemistry or biology) of the 330,000 copies per microgram of your sequence of interest would reside on the same size piece and could be moved by an electric current through a polymeric gel which had the property of resisting the movement in the current of larger sized fragment more than smaller ones such that after maybe an hour or three you could know that your particular sequence should now occupy a specific space and time. This was good.
But you also knew that there would be another 330,000 copies of at least another thousand different sequences right there at the same place in the gel and in the same amount as your sequence of interest. It was even more complicated than that, but that was enough to drive Cohen and Boyer in the late seventies to invent the frightening biological process of molecular cloning. It was called recombinant DNA. Glossing over the details, which were labor intensive (nothing like building a pyramid of course) and slow relative to chemical reactions, cloning allowed the problem of isolating a human gene from human DNA to be reduced to the problem of isolating it from a plasmid.
A plasmid is about a million times less complex than human DNA, and importantly, certain bacteria can be induced to reproduce plasmids along with themselves, doubling their number about twice per hour.
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Some Questions About PCR
How has PCR affected the medical world?
Far less than it has affected the medical journalistic world. The last time I was seriously hospitalized with coronary artery problems was 2004 and there was plenty of testing of blood and imaging work, but information about my DNA was not considered. This is still in the stage of research. It will become more and more a part of medical practice, since individual tolerance and susceptibility to certain drugs, like heparin for instance, is significant and connected to DNA genotype. Personalized medicine is coming. It is still in the research stage.
Transfusions of blood and organs are monitored for histo-compatibility using DNA types, and several genetic disorders as well as infectious diseases are certainly examined at the DNA level.
There is much more to come than has been applied. Practical medicine necessarily moves more slowly than medical research.
How did your life change after winning the Nobel Prize?
My favorite pastime is learning according to the directions I discover for myself. Having a Nobel Prize allows one to indulge this kind of habit without starving, and I have taken advantage of it. Some people are not so obsessed with their own freedom, and utilize the awarding of a Nobel as a gateway to power and responsibility, and the accompanying financial rewards. I don't accept responsibility easily and I am happy without those things. I like to read widely and at my own direction. Having a Nobel Prize has allowed me the opportunity to become well enough educated that I feel now that I really deserve one.
Tell us about this new discipline paleobiology?
It's not a new discipline, just newly invigorated. I had the good fortune to work down the hall from the great paleobiologist Allan Wilson when I was a graduate student at Berkeley and Allan was struggling with established conceptions about human origins and evolution in general. He needed better ways to measure real evolutionary distance than immunology provided, and I was thrilled to provide him with PCR, and he was thrilled to begin using it in his lab, which was one of the first to put it to any real use.
He thought I should have called it "in vitro cloning." I liked "Polymerase Chain Reaction.. The discipline of paleobiology would certainly not care to part with it now, under any name.
In your opinion what is the point where science meets with business. How can business affect the world of science?
I have never encountered a business person with any true interest in science. Why should he be interested? He had the choice, and he chose business. It is only through good fortune that money ends up in the hands of scientists, who know how to use it for anything other than making more money, and it is a sorry situation indeed, since much scientific research is not cheap.
Sometimes very fortunate scientists get rich, like Craig Venter, and then they can let their imagination direct their research, but this is the rare exception. Most scientists are constrained to do the bidding of businessmen, and it can be immensely frustrating for the scientist and unproductive for society in general. Most biological research ventures fail because the boss is highly subject to scientific illusions and has no idea how to separate truly good ideas from the highly simplified and often distorted things that filter up to him. He is usually under the influence of even less informed investors, and subject to misinformation from inferior scientists eager to have his favor. It is an unsavory world which I have never enjoyed.
As has been known for millennia "philosopher kings" are hard to come by Government grants, although offering, in theory, a preferable alternative, have the similar problem of being often administered by scientific incompetents who are after power and personal security, instead of widely useful knowledge. Good scientists don't like administrative jobs, which leaves us exactly where we are. Science is generally directed by non-scientists.
We stumble on.
Questions from Maria Vasilescu
