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Chapter 17 : From Diauxie to the Concept of Catabolite Repression
The most universally known and the most often misquoted is "Whatever is true for E. coli is true for an elephant." Jacques Monod's faith in the universality of the laws and mechanisms of biology contrasting with his provocative attitude of apparent cynicism in front of the great problems of "the secrets of life" was fascinating to those of us who surrounded him. Monod showed with Melvin Cohn that the kinetic parameters as well as the immunochemical properties of β-galactosidase did not change when a variety of inducers were utilized with the inducible strain or compared to the enzyme of the constitutive mutants, where no inducer was used. The rapid regulatory switches pointed toward an unstable intermediate embodying the genetic information between gene and protein. The intermediate, called "the messenger," soon became the messenger RNA, (mRNA). The progress of translation is independent of both the termination of the transcription and the survival of the initial end of mRNA. The survival of the initiating end of mRNA is independent of the intracellular concentration of inducer and largely, although not completely, independent of transcription. The mRNA is polycistronic and stays probably as a single piece for the major part of its functional lifetime. At the steady state of all processes, the polycistronic mRNA is, however, seldom integral. The major part of it should be pieces: some unfinished, some already missing the initiating end, some devoid of both, still growing on one side while losing the other side at the same speed.