[MUSIC] As you remember, last week, we discussed the structure of DNA and the double helix model proposed by Watson and Crick. Geneticists before that time were mostly arguing about a small number of items and mostly interested in a small number of questions. Morgan was mostly interested in the stability. What chemical structure can provide the stability required for faithful transmission from generation to generation. Mueller on the other hand, saw that the really interesting problem is not the stability, but the replication of the structure. And finally, there were a few other scientists who asked this question, what sort of structure must the gene possess to permit it to mutate, to give rise to mutants. And what are the conditions for mutants to occur and this is where today's story will start with a gentleman name Seymour Benzer. Seymour Benzer was a physics student. In 1942, he got a fellowship to go to Purdue, Indiana, and from 42 to 47, he was a PhD student in physics. He was working in what we would call solid-state physics and was mainly interested in improving radar detection systems and using germanium layers in the detectors. He was a very successful student and he was so successful that a few weeks after he got his PhD, he was offered a position as an assistant professor, that doesn't happen very often these days. What is even more unusual is that a few weeks after Benzer got his job, his job as a professor who was supposed to start a biophysics lab, he decided to go on a sabbatical. Usually, you take a sabbatical after six or seven years of performing your duties as professor. He took his sabbatical before he even started giving a class or a course. And not only did he leave for sabbatical, but he left for a sabbatical that would last for five years which is highly unusual. And what I think is extraordinary, interesting and telling is that the faculty at Purdue didn't fire him, didn't throw him out, but kept his position on hold until he would come back. That's quite remarkable. So Benzer goes to the phage course in Cold Spring Harbour, the 1948 phage course. And then he moves to a place where physicists interested in biology could work named the Oak Ridge National Lab. He was mostly working on nuclear reactors and nuclear materials, but had a small biology division. And he likes it there. He starts to work on UV effect, UV radiation on living particles and very shortly after, moves to Caltech, in Max Delbruck's lab. Now, Max Delbruck's lab at the time, was a very flourishing lab. And among the people who were working with Benzer, was a man named Renato Dulbecco, who would win a Nobel Prize for his work on animal viruses later on. Who is known by everybody who has ever worked with a mammalian tissue culture system, mice, human, rats, etc. Because all these cells are grown usually in a medium called Dulbecco's Modified Eagle Medium, DMEM. So a lot of the students have seen this. Not many usually realize that Dulbecco was not only famous for making a medium, but also for doing science. At the time Benzer arrives at Caltech, comes another visiting professor. Another professor on sabbatical, this one is Andre Lwoff who comes from Paris and who is the pioneer of the molecular work on lysogen. And Delbruck is very keen on taking people out for walks in the desert and all the lab has to go on the walks. And on one of the walk, he takes Lwoff, Lwoff's wife. No, Lwoff's wife wasn't there, Benzer, Benzer's wife. And Benzer's wife who was a nurse has absolutely no interest whatsoever for walks in the desert. And Lwoff being a French Parisian, has not much interest in going out in the desert either. And so Madame Benzer and Monsieur Lwoff stay behind and chat. And at some point, Madame Benzer says, Sermour would like so much to go to Paris and if we could spend a year there. No problem, he can come to my labs, and be very happy. And then at that time, they realized they're lost, they're lost. They've lost the other people. They're lost in the middle of nowhere in the desert in California. Well fortunately, there were other people in the desert that day. There were a group of hunters and the group of hunters bumps into them and says, why do you make so much noise? You're scaring the game, and they were lost. And so the hunters were kind enough to take them back to the parking lot and delivered them back to the party, and Delbruck says, where did you go? Few days later, Seymour Benzer receives a letter from Andre Lwoff. They're in the same department, basically next to each other. Saying that he's invited to come and spend a year from 51 to 52 at the Pasteur in Andre Lwoff's department. So there they go, and the Benzers arrive in Paris and they're very happy to be in Paris. And Benzer starts an experiment that is a bit weird, but it's a trial. They know that if you infect a bacterium with a virus, with a phage. And the bacterium is physiologically silent, inert, not happy, without food, starved, whatever you want to call it. The bacterium will not support the phage growth. You will not get a phage progeny. On the other hand, if you infect the bacterium that is happy and not starved, you would get a phage yield. So Benzer notes that the people at the Pasteur are also working on enzyme induction, we'll see the lac system toward the end of the class. And what he decided to do was take a cell that uses lactose as a carbon source. That can use lactose as a carbon source, but is not induced and is starved for glucose or other food. And his idea is to see whether you can infect with a phage, a star cell. And then, bring the star infected cells onto a medium where lactose is present. In the hope that you could use the lactose gene, restore happiness for the bacteria and of course, yield phage, progeny. So the first experiment is done along that line and he uses a strain that is a lambda lysogen strain of E.coli, K12 lambda. And he gets nothing, no growth, not even in the control, because the phage he'd used was a T4 R2 mutant. And so he sees the phenomenon that will make him famous. And doesn't realize it's potential. Something must have gone wrong, so he uses another strain, E.coli B and then the experiment worked and at the end, the experiment is a failure. This notion of inducing after infection doesn't work. He forgets about that. 1952, he goes back to Purdue, starts his classes and there he has the job of teaching biology to physics and biology students. And setting up a lab and starting his own experiment. And he's also supposed to do practical experiments with the students, what we call, [FOREIGN] in French. So he has all these things to do at the same time, which is a little bit tough. And the question hanging around the paper of Watson and Crick has appeared, how large is a gene? How does it fit with the size proposed by Zimmer and Timofeeff and Delbruck? What is the shape of the gene? And the shape of the gene is something that was not at all clear. Of course, the double helix suggests that the shape of the gene is a linear array of nucleotides paired to each other. To the complementary. So at that time he has on one side, T2 or T4 R2 mutants, white type. And he's also preparing a class for the students where they will use a lambda lysogen and a non lysogen to see how they respond to uv light. And since he has the cells, he decides to plank his stock of phage on these cells and this time, he observes the phenomenon. The R2 mutants don't plate on what we would call K lambda, but they do plate on K and then, he really realizes what's going on. Later on in the reconstruction, in the imaginary reconstruction of the events, he would say that he realized all at once the potential of this observation. Well if you think of two years before, he was in Paris and he didn't see it, so you can see. So basically, he has this observation and very quickly, he does the few control experiments that tell him what's going on. And he knows the numbers of phage particles he can plate. He knows all of that and has within a few weeks, the basis for his result.
