Professor Emeritus Franklin Stahl

The 1950’s saw a revolution in the field of genetics. Where once genetics was the study of Mendelian crosses and heredity, now it is the study of DNA. With his and Matthew Meselson’s discovery of semiconservative replication, Franklin Stahl cemented himself as one of the pioneering figures in this new field of Molecular Genetics. Their experiments, using heavy and light isotopes of Nitrogen to label newly formed DNA, established our current understandings of DNA replication. Yet, as Professor Stahl points out, his seminal role in Genetics was due less to his intellect than to chance encounters which shaped both his research and the field as a whole. Professor Stahl has graciously accepted an interview with the Journal of Undergraduate Research, to reminisce about his time as a graduate student at the University of Rochester, and to pass on a bit of advice to up and coming researchers.

As an undergraduate, Stahl initially intended to enter a medical program. However, his grades and interests led him to consider a Ph.D. instead. At the time, he had not had the opportunity to see what a laboratory was like, but he knew that if he was going to pursue a Ph.D. it would be in Genetics.

I didn’t like the Genetics course at Harvard; the Professor was boring. But I knew that genetics, Mendelian Genetics, was interesting. It was the predictability and orderliness of Mendelian Genetics that drew me to it; unlike many other subjects it was open to mathematical analysis.”

Professor Stahl entered upon graduate work at the University of Rochester. He had applied to the University pretty much with his eyes shut:

I had applied to three graduate programs, and the only one for which I had completed the application correctly was Rochester. The school did have a Genetics professor (Donald Charles), and I was accepted.”

The acceptance was a relief to Stahl, as he would rather be in the laboratory than be sent off to kill in Korea. However, when assigned to Professor Charles’ lab, he was not energized by what he found,

I didn’t really want to learn how to use antibodies to locate specific proteins within mouse cells. It’s important to recognize that if your first step in a career really sucks, find something more to your liking as soon as possible. At the time, I didn’t do that, but Professor Charles could see exactly what I needed and sent me to a place where I could study microbial genetics.”

The courses that Stahl took over the summer were Bacteriophage (Phage) and Bacterial Genetics at Cold Spring Harbor (CSH). The phage course was unusual, in part because of who was taking it. It was from this experience that Professor Stahl became hooked on phage biology.

The course was originally designed for atomic physicists, who wanted to learn molecular biology, so they could turn from studying death to studying life. This meant it was a rigorous course, which added excitement. I was captured by phage genetics, inspired particularly by the simplicity of the systems. In my mind, if the same basic processes happened in both phage and higher organisms, then studying phage, a system with few bells and whistles, could uncover the basic mechanisms of life. At the time, Professor Charles was suffering from Hodgkin’s lymphoma, which led him to withdraw from the laboratory. This fortuitously gave me the opportunity to transfer to another University, one that had a phage group.”

While Stahl applied for transfer, the University Department of Biology was looking to recruit new professors, and Stahl suggested Gus Doermann, who had been one of the instructors for the CSH phage course. Doermann was already well known for his work with T4 phage at Oak Ridge National Laboratory, and his recruitment to the University of Rochester halted all of Stahl’s plans to transfer. Stahl immediately joined the Doermann Lab, and Professor Doermann recommended that Stahl train at the dirty Oak Ridge lab before the transfer to the clean lab space in Rochester. Why did Doermann feel the need to have Stahl trained at Oak Ridge?

Gus (Doermann) wanted me to come to the Oak Ridge lab so that I could get trained on techniques and make my (likely radioactive) mistakes in the old lab. He was leaving that lab, so he didn’t care how much of a mess I made, but he didn’t want me making those mistakes in his new lab at Rochester.”

Professor Stahl finished his doctoral work at the Doermann Lab, perfecting his skills working with T4 phage, however, as the end was in sight, he ran into an issue with his qualifying committee:

I was all set to graduate, but my qualifying board wanted me to take physiology. I didn’t want to take it, because I did not respect the professor who taught that course. I told the Chair (of Biology) that there was no way that I was taking this physiology course. After some time, we agreed that I could be sent off to the Woods Hole Marine Biology Laboratory (MBL), to take the physiology course there.”

By luck, a lab section of the course was to be taught by Professor Jim Watson, and he was to be assisted by Mathew Meselson.

I was sent to Woods Hole, which gave me the good luck of getting to know Jim Watson better, and of meeting Matt Meselson. After completing my thesis, a year later, I drove to Caltech, the “Mecca of Molecular Biology”, where Max Delbruck and Linus Pauling had gotten biologists, geneticists, and biochemists all under the same roof,”

The stage was set for the seminal discoveries with Meselson. The idea of the final experiment was simple and beautiful: take bacteria grown in heavy 15N-containing medium, and move them into light, 14N medium, At intervals remove and lyse some cells and spin the lysate in an ultracentrifuge. Since, for replication to occur, new, light nitrogenous bases must have been produced. The new 14N or 15N would be incorporated into the bacterial DNA, and the relative amounts of each isotope in new duplexes could be measured. After one generation, which doubles the DNA, the same amount was incorporated into each of the daughter duplexes. Each of these two half-heavy duplexes gave birth to one light and one half-heavy duplex in the next generation of growth in the 14N medium.

If the two, complementary, strands of a replicating molecule were to stay bound together through replication, then a heavy 15N band would persist through multiple division cycles. However, if replication was semiconservative, where each parent strand is paired with a newly synthesized complementary strand, then a mixed band between 14N and 15N would be expected to persist. However, Meselson and Stahl did no such experiments with bacteria until after they tried an experiment with phage.

Obtained from Weaver Molecular Biology 5th ed.

So, we had just gotten a new ultracentrifugation machine, and we wanted to spin phage in a Cesium Chloride (CsCl) solution, because we knew that CsCl was just heavy enough (to separate 14N and 15N), and we had hoped to transfer the phage from bacteria grown in heavy nitrogen (15N) to light (14N) media. As a test, we tried to use the ultracentrifuge to separate the phage particles, but two things happened that we were not expecting. First, the CsCl moved, creating the gradient that was so crucial to the bacterial experiment described above. Second, the phage particles broke apart, making a band of something (that turned out to be DNA) in the middle. Soon after, the light-bulb went off and we switched to E. coli, successfully validating Watson’s semiconservative model of replication.”

Aftwards, Stahl moved to the University of Missouri. He wanted to start a lab of his own, and his family found the air in Pasadena unbearable:

The smog was bad in Pasadena, and we were just having kids. The air could not be good for them. In those days people burned their trash in backyard incinerators, so you can imagine how bad it was.”

Stahl thought Columbia, Missouri would be a respite from the smog, and a good place to raise a family. His sister-in-law had married a son of Professor Lewis Stadler, a renowned Geneticist at the University of Missouri.

My wife, Mary, had visited Columbia and thought it a pleasant place. Sadly, however, a litany of unpleasant issues emerged during our time there. We had just gotten to Columbia, and Mary needed clothes, so we looked for shops in the yellow pages. We kept seeing “White Clientele Only”. We didn’t like that, and came to understand that the town was seriously racist. Obviously, we could not raise our children there. There were problems on campus, too. I had been asked to teach the Introductory Genetics course for undergraduates. When I tried to teach Genetics, I started with Mendel, but it was too deep for many of them, and others already knew it. Consequently, I rewrote the course, so that these students could start from something simple but new to them, such as bacteria. I went through exponential bacterial growth, how that meant that bacteria must have genetic information, and I acquainted the students with these ideas. The Agriculture School faculty did not like that, they were fundamentally reactionary towards molecular genetics and wanted me to teach Genetics in the Good Old Way–Mendelism and heritability.”

A particular phrase stuck with Stahl:

Heritability, I was told, is the fraction of a hog’s price in the Chicago market that is ascribable to its genes.”

This led Stahl to think about other universities where he could establish his lab.

Word must have gotten out that I wasn’t very happy at Columbia (Missouri), because I was getting invitations to visit other schools. Cornell wanted me to visit, and Ithaca is a lovely place; Wisconsin wanted me to come, and so did UC Berkeley, but only Aaron Novick, from the University of Oregon, came to Missouri to put the heat on. Novick had recently accepted the responsibility of creating an Institute of Molecular Biology in Oregon, and while he was still considering whether he should do that, he asked Jim Watson for advice. First, Jim said that two positions is not enough for an institute, and that he should ask for double that at least, and hire Frank. So, Aaron came to Missouri to ask me to be the first guy on board, and he told me why I should sign up. He said that an Institute of Molecular Biology, as he envisioned it, would be Physicists, Chemists, and Biologists, all of whom were interested in understanding life at the molecular level, housed close to each other. They would share many facilities, centrifuges and other expensive things, so collaborative chemical, biological, and physical investigations that might not otherwise occur were facilitated, and that sounded exactly like what I needed. I felt comfortable with Genetics, but my Chemistry was minimal. (That was why I wouldn’t take graduate students at Columbia: I simply couldn’t find any chemists or physicists who could be collaborators). Aaron came to me with what I needed, convincing me to go to Eugene, Oregon, to look at the situation. Once you set foot in Eugene, you never want to leave: it is a beautiful place. Furthermore, I could live in the forest, within bicycle distance of my laboratory. I couldn’t find anything wrong with the invitation, so I became Aaron’s first appointment.”

At the University of Oregon, Novick and Stahl established a revolutionary institute for advancing Molecular Biology and Stahl soon turned his attention to an issue that was suggested by the results of his thesis work at Rochester: what, if any, relations were there between DNA replication and genetic recombination, the process(es) by which DNA swaps corresponding (ie, homologous) sections with each other. Professor Stahl aimed at getting to the mechanisms underlying this process using the CsCl gradient awareness he had gained working with Meselson and the demonstration by Jean Weigle at Caltech that viable Lambda phage could band nicely in a CsCl density gradient.

Led by Jette Foss’s (see below) pioneering explorations, Mary (my wife) and I, demonstrated reciprocal relations between replication and recombination with central roles played by ends of DNA duplexes.”

As things got rolling, Professor Stahl finally felt comfortable establishing a lab. The process was aided by Professor Novick, who knew that his primary job was not his research, but that of supporting the professors he had hired. Soon, Stahl opened his laboratory and “recruited” his first student:

The first day I was in my laboratory, a young lady entered, approached me, introduced herself and asked if she could work in my lab. It turned out the student, Jette Foss, was from Holland, and had been through the starvation of 1945. She was such a crackerjack student that they threw her out of high school in Salt Lake City, and facilitated her entry into the University of Utah, where she progressed toward a bachelor’s degree and got married. Circumstances brought her husband to a Chemistry job in Oregon, and she came with him. Before I had come to Oregon, she had been working with a geneticist who was famous, but not a good guy, and she was the kind of person who made her thoughts clear when she thought something was wrong. As soon as my feet hit the ground, she left his lab, and come to mine. She didn’t want a Ph.D., she just wanted to work in my lab. That’s attractive. She doesn’t need a project that is more or less certain to give a thesis. Instead, she could try to go for a deep understanding in one big leap. Even if she fell, she will have learned a lot and could try again. One day, after about a year and a half, she came to me and said “my husband is leaving, and we are going to Iowa in about 5 months, and I do want a Ph.D.” That’s a problem. I had to find her a Ph.D. question that she could take with her. I had one. It was a question that Max Delbruck said needed to be answered, or he would never believe that T4 phage had a circular linkage map, a linear chromosome, with a circularly permuted sequence and terminal redundancy. The goal was to show the circular linkage map using data from just one cross. What she needed was faith, courage, industry and brains (her cup of tea) plus a fourth genetic mutation (marker), which was provided by colleague George Streisinger. With that she went off to Iowa. In 2 years, she had her thesis, came back to defend, and got an Oregon Ph.D. Years later she returned to volunteer in my lab.”

Pushed by his students, Stahl had started moving into yeast in order to probe the complexities of this “higher organism”. Why look at these higher-level organisms if the basic mechanisms are still the same?

There is some stuff that complicates the issue, but the basic thinking of how the DNA molecules react to each other, are similar. In yeast, you get to deal with interference, where a crossover event in one region reduces the likelihood of a crossover in another region on the same chromosome. No such “interference” has been found in phage. However, as with phage, I was pecking away at what was required for crossing over, and then relating what I saw to the double helix. Jette loved the work, and she was GREAT at it.”

At Oregon, Stahl initially taught a couple of advanced discussion groups, but ended up teaching the introductory Biology course.

My job was to present an introductory Biology course that was future looking. You can’t teach this kind of Biology course to freshmen, because Chemistry is a prerequisite. My course started with microbes, followed with the genetics of eukaryotes, and then got into evolution, first in microbes and then in the analysis of evolution and speciation of the classical sort, as it is understood in higher organisms. After evolution, the course would go into physiology, and by then, students will have enough genetics and enough chemical thinking, that they can handle physiology not at a descriptional level, but instead at an analytical level. For the good students, that worked well. However, some students got blown out, because it wasn’t what they had in mind when they signed up for a biology course. They wanted to study flowers or cross-sections of root hairs, or something like that. They disappeared. Soon the course gained the reputation of being a good course where you had to work. Once the medical school had heard about it, they told students to take that course, or don’t apply to the UO medical school.”

Stahl also tried to promote that same level of analytical understanding in the undergraduates who came to his lab.

Undergrads in my lab would work on a phage or yeast question. They would be initiated into the underlying principles of the work, and were expected to pursue their research with those in mind. Often, they rose to this challenge and went on to graduate schools. I never had more than 6 undergraduates in my lab, and we had group meetings with them. We tried to integrate them into the ongoing research, and they would pick up a piece of it, which they identified as their own. When I was close to retiring, I had no graduate students but I had four undergraduates, all working on different aspects of a question identified by Dr. Foss, that first Ph.D. student, who became a volunteer in the laboratory after returning from Iowa. She had taken on these undergraduates, but they were pretty independent. Once she pointed them in the right direction, they were collecting the data and trying to get enough of it to allow meaningful statistical analysis. In the middle of that effort, I decided that I was too tired to go on, and that I would close the laboratory in June, giving them just a few months warning. For a moment they looked panicked, but got together and decided which of the experiments they would triage and which ones they would finish and interpret before the lab closed on June 1st. Without further input from their mentors, they completed and analyzed the experiments, which we wrote up after we closed the lab. They had done such a fine job organizing and analyzing that we published. When these kids came looking for letters for graduate school, it was great fun to write them. It works to take on undergraduates, as long as you give them a direction which is analytical and challenging enough to get them hooked. It’s DNA after all, it can’t be that complicated. I really liked how they cooperated; when they knew they didn’t have much time, they adjusted responsibilities. The student who was good at tetrad analysis, became the volunteer tetrad dissector for projects in need; the guy who was good at other stuff took that stuff. It was just wonderful, I never felt better in my life, to see what undergraduates could do, when you give them a bench, elementary instruction, direction and get out of their way”.

Some Quick Questions:

JUR: What is your favorite Molecular Biology/Genetics Textbook?

Stahl: I haven’t been keeping up with the textbooks that are coming out, but I still like the first book that I wrote: The Mechanics of Inheritance. Let me tell you a story about that. The book came out in 1953, and it taught Genetics starting small: essentially bacteria, transformation, phage, and then building up to Mendel’s garden peas. The book was reviewed by Science. It’s usually quite an honor to be reviewed by Science Magazine. So, I was flattered that they chose it, and they chose it as their chief review. However, the reviewer was a sharp man. He had no sympathy for my science, and he didn’t like my style of writing, because it wasn’t dignified. Of course not; I was writing for students, not for a reviewer who thought himself so important. I thought the review might kill the book. It didn’t, but I was at CSH several days after the review came out and got an independent opinion. It was end of season and I was at the abandoned beach with my two little boys. After a while, I saw a small figure walking down the beach, obviously straight toward me. I recognized her as Barbara McClintock, with whom I was friendly. She sat with us and opened with “Franklin, I know it must be hurting you, but you mustn’t worry about it. In a few years people will have forgotten what a really BAD BOOK it is.” After I caught my breath, I asked Barbara what she didn’t like about it? “Franklin,” she said, “you’ve taken all the mystery out of it.” The several times I went to CSH thereafter, I tried to get one up on her: “Barbara, why did you write your papers in such a way that no one could understand them?” and she responded “I surely didn’t write them for YOU to understand.” Another time: “Barbara, why did you such and such?” and she asked “Franklin, will you never grow up?” Anyway, I still like that little book, it has to be updated since we know so much more, but I think it takes the right approach to Genetics. Now, the trouble with up-to-date books is that they tend to get bigger and fatter. Soon the student drowns in them, too many pages of stuff; my book was small and focused on the essentials.

The Mechanisms of Inheritance by Franklin Stahl, can be found at Carlson Library on River Campus.

JUR: What is your favorite animal as a pet?

Stahl: I love the llamas! We’ve had 4 llamas in our pasture, but now we are down to one llama because I am getting old, and the llamas get old and die. The one llama we do have is beautiful. She got untrained when one of my caregivers started feeding her when she was out of the barn. So, the caregiver is in the process of retraining her, to get her used to feeding in the barn. That way, when the veterinarian comes for the biannual checkup, we will be able to get her (the llama) in the barn for her shots and stuff. She’s made great progress, on the first trip she wouldn’t do it, but by the fourth or fifth trip she was comfortable and went right into the barn. They learn fast (just like undergraduates). They are great pets, they are friendly, they are sociable, and they don’t spit at you unless you spit at them first.

JUR: What is your favorite model organism?

Stahl: Phage Lambda, it’s beautiful. If lambda goes into a cell and there are lots of other lambdas, they immediately recognize that life outside is not good, and if they go outside the cell, it will be slim pickings, because the bacteria will all be dead by now. So, what do we do? Alright, we make a truce, and one of us (who is lucky) will integrate into the bacterial chromosome, and be carried in the bacterial genome, until we (lambda phage) change our mind. The lambda phage and bacteria enter a deal, as long as the bacteria keeps multiplying in a happy way, any other lambda phage enters the cell, the integrated phage lambda will paralyze it. It’s basically a protection racket. If only one lambda finds itself in a bacterium, then it knows that there must be a lot of bacteria around, so it eats the bacteria, and gets on with the job of procreating and making 200 progeny. It does this until the bacterium is so scarce that it finds itself in the other situation, and they then hunker down. This first option, where lambda integrates into the genome, is the lysogenic phase, and the second option, where the virus gets to procreating, is the lytic cycle. Lambda phage is a temperate phage, which switches between the two. Now, there is also the option where the bacterium carrying the lysogenic-dormant lambda is in the sunlight for too long, and can no longer replicate efficiently. Now the deal is off, and lambda kills that bacterium, like a rat jumping off a sinking ship. Now, something that small has figured this out, through evolution of course, but it seems so smart that you have to study this phage.

JUR: If you were to restart your research career today, what would you study?

Stahl: I would first probably look at lambda, because lambda probably has a few tricks which it hasn’t shown us yet. On the other hand, the competition is very steep in phage lambda, because a lot of people feel this way about it. We did accidentally find something else about phage lambda, and the fact that we could just stumble onto this confirms that there must be more to lambda. It started when we looked at these very sick lambda mutants, which had a knockout of Rec (the bacterial recombination machinery) and gamma (an important repair factor). During replication one prong of the fork formed can break off, due to the complexity of moving the fork in the same topological direction, in addition to the size of the bacterial chromosome. The recombination machinery puts the fork back together by having gamma grab a very lethal Red recombinase. By doing this, gamma turns Red recombinase, which normally induces double-strand breaks, into a repair enzyme that fixes the fork using recombination. In the mutants, there was no gamma factor to “tame” Red recombinase, and no bacterial machinery to help gamma out, so the colonies did not grow so well. An undergraduate took the little titers they could get from the colonies and kept recycling them. Eventually, they started to grow, what they had done was select for a mutant in lambda which had allowed for the phage to be rescued from loss of gamma. There were 4 mutants that were found, all of which produced a specific sequence, and it was found that not only did that sequence tame Red recombinase, but also was found in the E. coli genome. Without looking in lambda, we would have never expected, or looked, for such a thing.

Professor Stahl now takes up his time investigating Israeli-American relations, spending time with his llamas, and occasionally has the pleasure of corresponding with his old colleagues.