Hamilton Smith on Post-doc with Mike Levine: P22 & the Int Gene
  Hamilton Smith     Biography    
Recorded: 03 Mar 2006

So at Ann Arbor I started in July of 1962. I had to complete my complete residency. They wouldn’t let me leave early. In fact, the professor of medicine said that I would thank him later on because once I’d finished the two year fellowship, I would be board qualified, I could come back and pursue my medical career. Which I found to be quite interesting, I enjoyed it immensely. But science was where it was at for me. So, when I—I’m really making a long story out of this, but when I went to Mike’s lab, finally, after corresponding with him for about a year—you know, I went in there with not really any kind of a clue as to what the relationship between a post doc and the mentor was supposed to be, because I hadn’t been brought up in that—I mean, I wanted to just go in there, he was providing me space and materials to do what I wanted to do. That was my attitude. So, he had proposed an experiment for me to start on, and I didn’t do it. You know, I said, "Well I want to try some of this other stuff first." So I started working on extracting DNA out of T4, and I was trying to visualize DNA strands in a fluorescent microscope. I can remember telling my wife shortly after I started that that I had just achieved something that they’d been trying to do for years. Of course I was wrong, but—she was very impressed, you know. Actually I was looking at a bottle of fobers/ Of course I wasn’t using ethidium, which probably would have worked. I was using a fluorescently-labeled methylated albumin that would stick to the DNA, something that Hershey developed at Cold Spring Harbor.

Anyway, I worked I guess about a year. I finally did the one experiment that he suggested and it didn’t give any real result. But I worked about a year, just doing what I wanted to do. It was mostly on recombination. And Mike was—he never said a word, he didn’t complain. We got along great. Then he had urged me to publish some of the stuff that I had, but I wasn’t satisfied that it really was good enough. What I was trying to do at that time was to density—to take phage that was completely density-labeled, put it into a cell – two different marked ones – and then isolate recombinants that were completely heavy. It was sort of like some of the Meselson work. But I wanted—I was trying to strive for sort of a clean result that would indicate some sort of a break and rejoin mechanism, but I never got better than 90 percent, or 80 percent. It wasn’t a clean result, and I just wasn’t in the mood to publish it.

So, then finally I got on to some work that he was interested in, studying what happens when you infect Salmonella typhimurium with a P22 virus that has mutations in the lysogeny so that instead of becoming a prophage it lyses the cell – the clear mutants. Very analogous to lambda. At that time there was a new technique that I’d just read about which was pulse labeling, using tritiated thymidine. And Mike wasn’t using it and I said, "Well, why don’t I do an infection, and then every minute I take a sample and do a 30 second pulse and we’d look at what happens to DNA synthesis"—in fact viral-specific DNA synthesis if possible because, actually, the DNA synthesis of the cell shuts off so you’re pretty much looking at the viral synthesis. And I got some really interesting results. If the cell was going to lysogenize it would very quickly synthesize some viral DNA and then it would shut off, and then as the prophage became incorporated and the bacterium started growing again, it would go on up. The mutants were interrupted at different points in the synthesis cycle. So, together we wrote up—I did all the experiments myself, but I had never written a paper, and Mike was extremely helpful, putting this into some sort of reasonable framework. That was a very valuable experience for me, writing that first paper.

So we published in the Proceedings, and I guess my career was on the move at that point. It was 1964 in Proceedings. I was the first author and Mike was the second author.Anyway, that, for me that was a major event, my first publication.

Then—so, Mike at that time was collecting—he had a couple of technicians that would pick temperature-sensitive phage mutants. And so we got temperature-sensitive C1, C2, C3 mutants - the same ones that we had studied for the DNA synthesis. And we showed again by heat pulse experiments, the same sort of kinetics. So it made a really nice second paper that we put into "Scienc"e. That was also—that came pretty quickly, I think, it was probably in ‘64 also.

Then I had heard Alan Campbell talk in 1962 - my first Cold Spring Harbor phage meeting - about his model for circular integration of prophage, and how the map order changed from that of the vegetative multiplying virus—became a circular map. And I thought, well, we should do the same thing for P22 and see if we can prove that it actually is going in the same way and forms a ___ map. So I did—this was some real genetics, you know, mapping markers along the phage chromosome. And that work was published in—I think we put it in "Genetics" around 1965 maybe. Then after that Mike went to—OK, then I had noticed a very interesting phenomenon, when you—I had—there was a mutant that I’d isolated that, uh – I’m trying to reconstruct it now here – that didn’t lysogenize, and then it sort of diluted out of the cells. You know, it was repressed, and it didn’t lysogenize and it didn’t—it’s been so long now. It’s one we called a maintenance mutant. But the plaques—actually the colonies, the colonies of infected bacteria were very mottled. I’m trying to reconstruct this now, let’s see. Anyway, on the basis of that observation, I thought I had a way of selecting for non-lysogenizing mutants, that were not just interrupted in the beginning stages but at a later stage. Turned out it was the integration function. They were amp-minus. They repressed in everything. They went through the normal cycle, but the virus never got into the chromosome. And I noticed this peculiar property; of course I didn’t know that this colony motteling was due to that at the time.

I isolated a number of these what I called L-mutants; later on they were called M-mutants, when they were subsequently found in lambda. So I studied their properties and published that in 1966, I think, or ’67, I’m not sure which. That was the first paper where I didn’t put Mike’s name on it, because—which was probably not a nice thing to do. I did all the work. He was in Geneva on his sabbatical, and I figured— Mike never said a word. I can remember sending it out for review, and even though Mike’s name wasn’t on the paper, they sent the reviews back to Mike, because the reviews went to people that, you know, knew him very well.

I was a post doc for two years and then a research associate for three years. In fact he had to shove me out the door. I would have stayed there forever. Because it was a perfect life. I could do pretty much what I wanted. I didn’t have to do any—I did a little bit of teaching, but I didn’t have to worry about the grants or any of that stuff, which I never wanted to do anyway. I could just work in the lab, checking out my ideas and what not. But finally he was getting very nervous my last year or so, and he began to say, “well, you know, at Cornell they have a position open.” So I flew out and they wanted me to teach an introductory class to five hundred students and I said, “no way.” Then I went to University of Pittsburgh, the medical school, Microbiology Department, almost accepted that, because being a medical school there would be much less teaching. Then a friend of mine at Ann Arbor, whose name slips me right now, he had a Hopkins connection and he had told them there was this guy out at Michigan that they should look at – and, of course, I had gone to school there. So they asked me to come out and give a lecture, and of course immediately I knew that was it.

In fact I remember after my lecture – this was in 1966, actually – I remember after my lecture that my wife and I went out to the Chairman’s, Barry Wood, the Chairman’s home, which was out in the country, very nice. We were sitting on the porch having drinks. It was I think May or June, very pleasant weather. He said, “Ham, what do you think, how do you like it?” I said, “I’ll take the job.” And he said, “No, no, hold it.” He says, “I want you to think about it for a few weeks, and then I’ll make an offer and you accept it.”

Hamilton Smith is a U.S. microbiologist born Aug. 23, 1931, New York, N.Y. Smith received an A.B. degree in mathematics at the University of California, Berkeley in 1952 and the M.D. degree from Johns Hopkins University in 1956. After six years of clinical work in medicine (1956-1962), he carried out research on Salmonella phage P22 lysogeny at the University of Michigan, Ann Arbor (1962-1967). In 1967, he joined the Microbiology Department at Johns Hopkins.

In 1968, he discovered the first TypeII restriction enzyme (HindII) and determined the sequence of its cleavage site. In, 1978 he was a co-recipient (with D. Nathans and W. Arber) of the Nobel in Medicine for this discovery.

He is currently the Scientific Director Synthetic Biology and Bioenergy Distinguished Professor at the J. Craig Venture Institute in Rockville, Maryland.

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