A fortunate journey on uneven grounds.

I was surprised to be invited to write a prefatory chapter for the Annual Review of Microbiology. Indeed, I did not feel that I belonged to that class of eminent scientists who had written such chapters. Perhaps it is because I am a kind of mutant: In spite of having experienced war, both German and Soviet occupations, repeated bombardments, dictatorships, and a revolution, I managed nonetheless to engage in scientific research, thus realizing a childhood dream. After having obtained my Doctor Rerum Naturalium degree in Budapest, Hungary, I was fortunate to meet Jacques Monod at the Pasteur Institute, and this became a turning point in my scientific career. In his laboratory, I contributed to the definition of the lactose operon promoter, uncovered intracistronic complementation in ß-galactosidase, and investigated the role of cAMP in Escherichia coli. In my own laboratory, together with many gifted students and collaborators, I studied the role of adenylate cyclase in bacterial virulence. This allowed the engineering of recombinant adenylate cyclase toxin from Bordetella pertussis for the development of protective and therapeutic vaccines.

Escherichia coli and the Emergence of Molecular Biology.

The creation of the "Phage group" by M. Delbrück, S. E. Luria, and A. D. Hershey in 1940 at Cold Spring Harbor played a crucial role in the development of molecular biology. In the 1940s, working with Escherichia coli and its viruses, Luria and Delbrück discovered the spontaneous nature of bacterial mutations and Hershey described recombination in bacteriophages and demonstrated with M. Chase that the genetic material that infects bacteria is DNA. At the same time, S. Benzer defined the structure of a functional genetic unit and J. Lederberg and E. Tatum discovered sexual recombination between bacteria. Some years later, Lederberg's group discovered extrachromosomal particles, the plasmids, and a novel way of genetic transfer through bacteriophages, called transduction. In 1949, at the Pasteur Institute in Paris, A. Lwoff uncovered the mechanism of lysogeny. Shortly afterwards, F. Jacob and E. Wollman unraveled the mechanism of the sexual process in E. coli and established the circularity of the bacterial chromosome. In the 1960s, J. Monod and F. Jacob, by genetic analysis of the E. coli lactose system, proposed the operon model for gene regulation and introduced the concept of messenger RNA. The elucidation of the double helix structure of DNA in 1953 by F. Crick and J. Watson had major consequences: the establishment of the copying mechanism (Meselson and Stahl), the discovery of the nature of the genetic code (S. Brenner) leading to its deciphering. E. coli and its phages were instrumental in the development of recombinant DNA technology based on the discovery of the restriction-modification system by W. Arber.

Jacques Monod, 1910-1976: his life, his work and his commitments.

Even today, the concepts developed by Jacques Monod during the course of his career remain at the core of modern biology. Looking back, Jacques Monod stands out as one of the giants who most strongly marked twentieth century science. He was endowed with intelligence, rigor, creativity, a relentless sense of deductive reasoning and a love of scientific elegance. His name will remain intimately associated with the birth, development and triumph of molecular biology. He was not only a brilliant scientist, but along with that he was a generous laboratory director who gave selflessly to his many students and co-workers. Yet in our minds, he will also remain a man with a profound moral commitment to any cause which he felt just. He was a true humanist.

Escherichia coli and the French School of Molecular Biology.

André Lwoff, Jacques Monod, and François Jacob, the leaders of the French school of molecular biology, greatly contributed between 1937 and 1965 to its development and triumph. The main discovery of Lwoff was the elucidation of the mechanism of bacteriophage induction, the phenomenon of lysogeny, that led to the model of genetic regulation uncovered later by Jacob and Monod. Working on bacterial growth, Monod discovered in 1941 the phenomenon of diauxy and uncovered the nature of enzyme induction. By combining genetic and biochemical approaches, Monod brought to light the structure and functions of the Escherichia coli lactose system, comprising the genes necessary for lactose metabolism, i.e., ß-galactosidase and lactose permease, a pump responsible for accumulation of galactosides into the cells. An additional genetic factor (the i gene) determines the inducibility and constitutivity of enzyme synthesis. Around the same time, François Jacob and Elie Wollman dissected the main events of bacterial conjugation that enabled them to construct a map of the E. coli chromosome and to demonstrate its circularity. The genetic analysis of the lactose system led Monod and Jacob to elucidate the mechanism of the regulation of gene expression and to propose the operon model: a unit of coordinate transcription. One of the new concepts that emerged from the operon model was messenger RNA. In 1963, Monod developed one of the most elegant concepts of molecular biology, the theory of allostery. In 1965, Lwoff, Monod and Jacob were awarded the Nobel Prize in Physiology or Medicine.

Relief of catabolite repression in a cAMP-independent catabolite gene activator mutant of Escherichia coli.

We isolated and characterized a new catabolite gene activator mutant (crp*) of Escherichia coli that confers cAMP-independent expression and total relief of catabolite repression of beta-galactosidase and tryptophanase synthesis. The two mutations responsible for this phenotype change the amino acids at codon 72 from Glu to Ala and at codon 144 from Ala to Thr in the corresponding CAP* protein.

Two-hybrid systems and their usage in infection biology.

Two-hybrid systems are powerful tools to study protein-protein interactions in biological systems. The role of protein-protein interactions involved in pathogenesis of bacterial and viral infections were defined by using yeast or bacterial two-hybrid screens. Examples are given to highlight the specificity of interactions in signaling pathways, in regulation, secretion and structure-function relationships of virulence factors and their cellular targets. Two-hybrid systems were also used to establish large-scale protein interaction maps of viral and bacterial pathogens, that might be useful to identify targets for new drugs or vaccines.