Werner Arber – Autobiography
I was born on June 3rd, 1929 in Gränichen in the Canton of
Aargau, Switzerland, where I went to the public schools until
the age of 16. I then entered the gymnasium at the Kantonsschule
Aarau where I got a B-type maturity in 1949. From 1949 to 1953 I
studied towards the diploma in Natural Sciences at the Swiss
Polytechnical School in Zurich. It is in the last year of this
study that I made my first contacts with fundamental research,
when working on the isolation and characterisation of a new
isomer of Cl34, with a halflife of 1.5 seconds.
On the recommendation of my professor in experimental physics,
Paul Scherrer, I took an assistantship for electron microscopy
at the Biophysics Laboratory at the University
of Geneva in November 1953. This laboratory was animated by
Eduard Kellenberger and it had two prototype electron
microscopes requiring much attention. In spite of spending many
hours to keep the microscope "Arthur" in reasonable
working condition, I had enough time not only to help developing
preparation techniques for biological specimens in view of their
observation in the electron microscope, but also to become
familiar with fundamental questions of bacteriophage physiology
and genetics, which at that time was still a relatively new and
unknown field. My first contribution to our journal club
concerned Watson
and Crick's
papers on the structure of DNA.
In the 1950's the Biophysics Laboratory at the University of
Geneva was lucky enough to receive each summer for several
months the visit of Jean Weigle. He was the former professor of
experimental physics at the University of Geneva. After having
suffered a heart attack, he had left Geneva to become a
researcher at the Department of Biology of the California
Institute of Technology in Pasadena. There, he had been
converted to a biologist under the influence of Max
Delbrück and had chosen to study bacteriophage lambda. This
is why the first electron micrographs of phage lambda were made
in Geneva. Stimulated by Jean Weigle we soon turned our
interests also to other properties of lambda, and the study of
defective lambda prophage mutants became the topic of my
doctoral thesis.
In the summer of 1956, we learned about experiments made by
Larry Morse and Esther and Joshua
Lederberg on the lambda-mediated transduction (gene transfer
from one bacterial strain to another by a bacteriophage serving
as vector) of bacterial determinants for galactose fermentation.
Since these investigators had encountered defective lysogenic
strains among their transductants, we felt that such strains
should be included in the collection of lambda prophage mutants
under study in our laboratory. Very rapidly, thanks to the
stimulating help by Jean Weigle and Grete Kellenberger, this
turned out to be extremely fruitful. We could indeed show that
lambda-mediated transduction is based on the formation of
substitution mutants, which had replaced a part of the phage
genes by genes from the bacterial chromosome. This made the
so-called lambda-gal phage derivatives so defective that they
were not able any longer to propagate as a virus. In fact, one
of the at first sight rather frustrating observation was that
lysates of lambda-gal, which indeed could still cause the
infected host cell to lyse as does wild type phage lambda, did
not contain any structural components of lambda (phage
particles, heads or tails) discernible in the electron
microscope. This was the end of my career as an electron
microscopist and in chosing genetic and physiological approaches
I became a molecular geneticist.
After my Ph. D. exam in the summer of 1958 I had the chance to
receive an offer to work at the University
of Southern California in Los Angeles with Joe Bertani, a
former collaborator of Jean Weigle. Several years before,
Bertani had isolated and characterised another bacteriophage of
E. coli, P1. Phage P1 rapidly had become a very welcome tool
of bacterial geneticists, since it gives general transduction,
i.e. any particular region of the host chromosome gets at some
low frequency wrapped into P1 phage particles if P1 multiplies
in a cell, and this enables the geneticists to carry out linkage
studies of bacterial genes. While working as a research
associate with Bertani, I received P1 at first hand which
enabled me to study phage Pl-mediated transduction of monomeric
and dimeric lambda prophage genomes as well as of the fertility
plasmid F.
In the meantime, my Ph. D. thesis on lambda-gal, although
written in French, had been read, or, what is perhaps more
essential, understood in its conclusions by many leading
microbial geneticists.
This may be the reason why I received offers to spend additional
postdoctoral time in several excellent laboratories. On the
other hand, I had remained in close contact with Eduard
Kellenberger, and he urged me to come back to Geneva in order to
lead an investigation on radiation effects on microorganisms. As
a compromise, I decided to return to Geneva at the beginning of
1960, but only after having spent several very fruitful weeks at
each of the laboratories of Gunther
Stent in Berkeley,
Joshua Lederberg in Stanford
and Salvador
Luria at the Massachusetts
Institute of Technology, Cambridge.
At the end of the 1950's, a special credit had been voted for by
the Swiss Parliament for research in atomic energy, including
radiation effects on living organisms. Eduard Kellenberger felt
that important contributions to the latter questions could be
expected from studies with microorganisms, and he had therefore
submitted a research proposal which found approval by the
granting agency, the Swiss
National Science Foundation. The project could bring insight
into the nature of radiation damage to genetic material and its
repair mechanisms, as well as of the stimulation of genetic
recombination by radiation. These topics had already engaged the
attention of Jean Weigle and Grete Kellenberger for a number of
years.
One of the first experiments after my return to Geneva was to
render E. coli B and its radiation resistant strain B/r
sensitive to phage lambda. The first step to accomplish this was
easy thanks to a hint received from Esther Lederberg to look for
cotransduction of the Ma1+ and lambdaS
characters. However, the strains thus obtained still did not
allow an efficient propagation of lambda. Very rapidly I
realized that this was due to host-controlled modification, a
phenomenon described for lambda and E. coli strains seven
years earlier by Joe Bertani and Jean Weigle. However, I was not
satisfied to know how to overcome this barrier. I was also
anxious to know how the restriction of phage growth and the
adaptation of lambda to the new host strain worked. When I
started investigations on the mechanisms of host-controlled
modification, I did not of course imagine that this sidetrack
would keep my interest for many years. Otherwise I might not
have felt justified to engage in this work because of its lack
of direct relevance to radiation research. However, a lucky
coincidence rapidly dissipated these concerns. At the same time,
Grete Kellenberger had looked at the fate of DNA from irradiated
phage lambda upon infection of host bacteria: part of it was
rapidly degraded after injection into the host. And so was the
DNA from unirradiated phage lambda used to measure adsorption
and DNA injection into restrictive bacterial strains! This
phenomenon became the topic of Daisy Dussoix's doctoral thesis,
who very carefully not only studied the DNA degradation of phage
that was not properly modified, but who also tried to detect
parallels between the fate of unmodified DNA in restrictive
conditions and of irradiated DNA in normal host cells.
Within about one year of study, it had become clear that
strain-specific restriction and modification directly affected
the DNA, without however causing mutations. It soon also became
obvious that restriction and modification were properties of the
bacterial strains and acted not only on infecting bacteriophage
DNA, but also on cellular DNA as manifested in conjugation
experiments. These findings were reported by myself and Daisy
Dussoix for the first time to the scientific community during
the First International Biophysics Congress held in Stockholm in
the summer of 1961. In a more extended version I presented them
in 1962 to the Science Faculty of the University of Geneva as my
work of habilitation as privatdocent. This work earned me in the
same year the Plantamour-Prévost prize of the University of
Geneva.
At a time before the Swiss Universities received direct
financial help from the federal government, the Swiss National
Science Foundation awarded "personal grants" to
qualified researchers to allow them to guide projects of
fundamental research at a Swiss University. I was lucky to
benefit from such a support form 1965 to 1970. These years were
devoted to hard work to consolidate the preliminary data and the
concepts resulting from them, and to extend the acquired
notions, in particular with regard to the mechanisms of
modification by nucleotide methylation, with regard to the
genetic control of restriction and modification and with regard
to the enzymology and molecular mechanisms of these reactions.
This work would not have been possible without a very fruitful
help by a large number of collaborators in my own laboratory and
of colleagues working on related topics in their own
laboratories. I was extremely lucky to receive in my laboratory
in the basement of the Physics Institute of the University of
Geneva a number of first class graduate students, postdoctoral
fellows and senior scientists. It is virtually impossible to
list them all in this context, but my warmest collective thanks
go to all of them. In 1964 Bill Wood laid out a solid basis for
the genetics of the restiction and modification systems EcoK
and EcoB. Later, Stuart
Linn, profiting from his fruitful contacts with Bob Yuan and
Matt
Meselson, who worked in the USA on the enzymology of EcoK
restriction, set the basis for in vitro studies with EcoB
restriction and modification activities. These studies
culminated in the final proof that modification in E. coli
B and K is brought about by nucleotide methylation. This concept
had found its first experimental evidence during my two months'
visit in 1963 with Gunther Stent at the University of California
in Berkeley. Several years later Urs Kühnlein, a Ph. D student,
and John Smith, working for various lengths of time with us,
succeeded in careful in vivo and in vitro measurements on
methylation to validate and extend the earlier conclusions.
Their experiments also brought important conclusions with regard
to the concept of the sites of recognition on the DNA for the
restriction and modification enzymes.
As an illustration that my work has not always been easy and
accompanied by success, I would like to refer to my long,
fruitless and thus largely unpublished attempts to find
experimental evidence for the diversification of restriction and
modification systems in the course of evolution. Systems EcoK
and EcoB form a closely related family as judged from
genetic and functional studies. Another family is formed by
restriction and modification systems EcoP1 and EcoP15.
One could expect that mutations affecting the part of the
enzymes responsible for recognition of the specificity site on
the DNA might result in new members of the family, recognizing
new specificity sites on DNA. We have in vain spent much time in
search for such evolutionary changes both after mutagenization
and after recombination between two members of the same family
of the above mentioned systems. That the basic idea for this
search was good was recently shown by Len Bullas, Charles Colson
and Aline van Pel (J. Gen. Microbiol. 95, 166- 172, 1976) who
encountered such a new system in their work with Salmonella
recombinants.
In 1965 I was promoted extraordinary professor for molecular
genetics at the University of Geneva. Not only did I always
enjoy a continued contact with the students, but I also
considered teaching as a welcome obligation to keep my
scientific interests wide. Although we had a few excellent
students in our laboratories, the teaching of molecular genetics
at the University of Geneva in the 1960's suffered a bit from a
lack of interest by the young generation. This might have been
related to a more general lack of public interest for this
field, which was perhaps due to the economic structure of the
city of Geneva and its environments. These, at that time perhaps
more subconscious concerns, might have helped me to accept in
1968 an offer for a professorship at the University
of Basel, since I felt that more general interest would be
given to molecular genetics in this city with a long tradition
of biomedical research at its industries.
I started my new appointment at the University of Basel in
October 1971 after having spent one year as a visiting Miller
Research Professor at the Department of Molecular Biology of the
University of California in Berkeley. In Basel, I was one of the
first persons to work in the newly constructed Biozentrum,
which houses several University Departments, in particular those
of Biophysics, Biochemistry, Microbiology, Structural Biology,
Cell Biology and Pharmacology. This diversity within the same
house largely contributes to fruitful collaborative projects and
it helps to keep horizons broad both in research and teaching.
Additional contributions to this goal come from contacts with
other nearby University Institutes as well as with the private
research Institutions in the city.
Since my coming to Basel, I devoted relatively little of my time
to further studies on restriction and modification mechanisms.
Not that I have lost my interest in them. On the contrary, I was
fortunate to be able to set up a junior group which under the
leadership of Bob Yuan and more recently of Tom Bickle, became
rapidly quite independent, and it continues to be very
successful in its investigations on the more detailed aspects of
the molecular mechanisms of restriction and modification. This
allowed me to turn my main interests back to other mechanisms
affecting either positively or negatively the exchange of
genetic material. For a number of years Nick Gschwind, a Ph. D.
student, and Dorothea Scandella, a postdoctoral fellow, explored
two other mechanisms found in some E. coli strains or
mutants and affecting more specifically than restriction and
modification systems particular steps in the propagation of
bacteriophage lambda.
For the last several years I have turned my principal interests
to the intriguing activities of insertion elements and
transposons, which by their actions on genetic rearrangements,
seem to be the main driving forces of evolution in
microorganisms. Because of their independence on extended
nucleotide homologies these forces bring about exchange of
largely unrelated genetic materials. Our postdoctoral workers
Katsutoshi Mise, Shigeru Iida and Jürg Meyer brought important
contributions to the understanding of these phenomena, mainly by
the use of the bacteriophage P1 genome as a natural vector of
transposable elements. But general knowledge on this to my mind
extremely important field is still very scarce and deserves
continued attention.
Solid notions on naturally occurring genetic exchange between
organisms that are not directly related will also form a good
basis for a scientific evaluation of conjectural risks of in
vitro recombinant DNA research. Since this research largely
makes use of restriction enzymes, although it in no way fully
depends on them, I consider it a personal obligation to
contribute to the best of my abilities to the solution of
questions which arose in the scientific and public debate on
this research in the last few years. I see two ways to reach
this goal. The first is scientific and tends as just stated to
better understand what nature does in its nonhomologous genetic
exchange. The second is rather political and it consists in
actions to stimulate continued awareness of responsibility to
work with a maximum of care in all scientific investigations,
which should, however, be allowed to be done under optimal
academic freedom.
A curriculum vitae would be incomplete without reference to my
private life. I am fortunate to have found a continued support
and steady encouragement by my family, in particular by my
parents, and, since we became married in 1966, by my wife
Antonia. In response to their interest and understanding for my
scientific activities, I have tried to give them my personal
affection needed for a harmonious life. Our two daughters Silvia
and Caroline were born in 1968 and in 1974, respectively. When
Silvia learned that I had been honored by the Nobelprize she not
only wanted to know what this is, but also why I was chosen as a
Laureate. After explaining her in simple terms the basic
concepts of the mechanisms of restriction enzymes, she, after
some reflection, reexpressed this message in her own terms by a
tale, which in the meantime has found wide diffusion around the
world. It might thus be justified to finish this curriculum
vitae by its reproduction:
"The tale of the king and his servants
When I come to the laboratory of my father, I usually see
some plates lying on the tables. These plates contain colonies
of bacteria. These colonies remind me of a city with many
inhabitants. In each bacterium there is a king. He is very long,
but skinny. The king has many servants. These are thick and
short, almost like balls. My father calls the king DNA, and the
servants enzymes. The king is like a book, in which everything
is noted on the work to be done by the servants. For us human
beings these instructions of the king are a mystery.
My father has discovered a servant who serves as a pair of
scissors. If a foreign king invades a bacterium, this servant
can cut him in small fragments, but he does not do any harm to
his own king.
Clever people use the servant with the scissors to find out the
secrets of the kings. To do so, they collect many servants with
scissors and put them onto a king, so that the king is cut into
pieces. With the resulting little pieces it is much easier to
investigate the secrets. For this reason my father received the
Nobel Prize for the discovery of the servant with the
scissors".
From Les
Prix Nobel 1978.
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