You have all heard about the DNA double helix and genes. Many of you know that mutations occur randomly, that the DNA sequence is read by successive groups of three bases (the codons), that many genes encode enzymes, and that gene expression can be regulated. These concepts were proposed on the basis of astute genetic experiments, as well as often on biochemical results. The original articles were these concepts appeared are however not frequently part of the normal curriculum of biologists, biochemists and medical students. This course proposes to read study and discuss a small selection of these classical papers, and to put these landmarks in their historical context. Most of the authors displayed interesting personal histories and many of their contributions go beyond not only the papers we will read but probably all their scientific papers. Our understanding of the scientific process, of the philosophy underlying the process of scientific discovery, and on the integration of new concepts is not only important for the history of science but also for the mental development of creative science.
Part 3
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Gave a good insight of the subject.So much of historical papers reviewed on one platform is really good.
Excellent course. It helped me a lot in understanding the classical experiments in detail.
The arabinose system represents the first demonstration of a positive regulation of gene expression. The first araC mutants do not synthesize any of the catabolic enzymes encoded by the adjacent araBAD genes. They also fail to express AraE, the main arabinose permease, whose gene is located on the opposite side of the bacterial chromosome, far away from the araCBAD locus. In this paper, Engelsberg et al. isolate and characterize constitutive mutants. They first show that all araC constitutive and negative mutants map to the same gene. They demonstrate a coordinate expression of all tested arabinose enzymes, including the distantly located permease; this expression is specific since the level of an unrelated enzyme and of a glucose permease are unaffected. Using partial diploids, they show that the araC negative mutants are recessive to both the normal gene and the constitutive mutants.These results are discussed in the context of the known mutants of the lactose system. Other interpretations of the results will be discussed.The pioneering work will be placed in perspective with what is now known about the regulation of the arabinose enzyme, including the fact that AraC is also a repressor, and that repression involves DNA looping between distant sites.
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Dominique Belin
Professor
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