Leo Szilard: a personal remembrance.

SINCE retiring as a full-time faculty member about ment of this building. Their plan was to study mutation in bacteria, and they looked for methods to measure 10 years ago, I have occupied myself with writing chronicles of past experiences. The first was an account mutation rates. At Cold Spring Harbor they had encountered Jacques of the advances made in the elucidation of gene expression and its regulation during the twentieth century Monod, who had told them about his diauxie experiments in which, in the presence of the two carbon (Maas 2001). The second was an account of the history of a Jewish family in the Palatinate region of Germany, sources glucose and lactose, glucose is used preferentially. Szilard was intrigued by this finding, and to anabased on a memoir written by my father after World War I (Maas 2003). Now, in looking for another chronicle to lyze it he and Novick designed an apparatus for the continuous culture of bacteria, which they called a write, I was very pleased to be asked to write a Perspectives essay about Leo Szilard. I could think of no better topic chemostat (Novick and Szilard 1950). Subsequently, this device turned out to be very useful for the study of and I accepted enthusiastically. I first met Szilard in 1951 and had many contacts with mutation rates, as well as for physiological studies on bacteria. Aaron Novick has given a vivid account of his him until the time of his death in 1964. During this period I developed an unreserved admiration for him association with Szilard during this period (Novick 1966). as a scientist and as a human being. I consider it a privilege that I now have an opportunity to describe this In 1951 I was working in the laboratory of Bernard Davis at Cornell Medical College in New York City. We unusual man as I remember him. Szilard started a new career in biology in 1947 after were studying various biosynthetic pathways of Escherichia coli with the use of mutants isolated in our laborahaving made significant contributions to physics and tory. Szilard was a frequent visitor and liked to discuss having been instrumental in the development of the our work with us. My own problem concerned the manatomic bomb. At that time he asked Aaron Novick, a ner in which genes control the production of enzymes, young physical organic chemist, to join him in his new as postulated in Beadle’s one gene–one enzyme hypothventure. Novick accepted enthusiastically, and this was esis. Do they determine the structure of enzymes or the beginning of an association that lasted over many merely the rate at which the enzymes are produced? years. They began their entry into biology by taking the To study this question, I used a temperature-sensitive phage course at Cold Spring Harbor in 1947, which at mutant requiring pantothenic acid for growth in which that time was taught by Max Delbrück (see Susman the enzyme affected by the mutation could be measured 1995). in extracts. I found that the extracted enzyme was much Novick and Szilard set up their own laboratory at the more heat labile than the corresponding enzyme from University of Chicago in 1948, where Szilard had been the wild-type strain. It seemed likely that the enzyme appointed a professor of biology and sociology. They molecule itself was affected by the mutation, but there became members of the new Institute of Radiobiology was the possibility that the observed difference was due and Biophysics, which was located in a former synagogue to an extrinsic factor produced in the mutant. I posed of a Jewish orphanage. Their laboratory was in the basethis question to Szilard, and he immediately suggested that I could get an answer by studying heat inactivation in mixtures of mutant and wild-type enzymes. I carried 1Address for correspondence: Department of Microbiology, New York out the experiments Szilard suggested, and the results University School of Medicine, 550 First Ave., New York, NY 100166402. E-mail: [email protected] showed clearly that the difference in thermal stability