Operon hypothesis

Analysis of Lactose Metabolism in EcoU Led to the Operon Hypothesis... 

Enhanced gene expression can be achieved by the addition of a promoter to the cloned gene. For example, the lac promoter may be added upstream of the protein DNA sequence, giving rise to the expression of the protein in the presence of lactose and in the absence of glucose, (cf. operon hypothesis Section S.7). 

The molecular and genetic relationship between enzyme induction and repression was clarified by the genetic research of Jacob and Monod at the Pasteur Institute, Paris (see reference l7>). Their classic work led them to develop the operon hypothesis for the control of protein synthesis in prokaryotes, which has since been verified by direct biochemical experiments. 

The Jacob-Monod operon hypothesis has provided a tremendous stimulus for investigations directed toward understanding not only the lac system but other genetic regulatory systems as well. 

H Genetic studies led to the operon hypothesis. Biochemical investigations were essential to provide direct evidence for the hypothesized properties of the repressor. The first task was to isolate the repressor. 

Schematic model illustrating the operon hypothesis. This diagram is modified from the original proposed by Jacob and Monod, who thought i gene repressor was an RNA rather than a protein, (a) The i gene encodes a repressor that binds tightly to the operator o locus, thereby preventing transcription of the mRNA from the z, y, and a structural genes. (b) When inducer is present, it combines with repressor, changing its structure so it can no longer bind to the operator locus. Inducer also can remove repressor already complexed with the o locus.

Jacob Monod Proposed the operon hypothesis and postulated the function of messenger RNA. 

Since R. rubrum is prokaryotic, this could be explained with operon hypothesis. As shown in Fig. 2, the expression product of regulating gene, the repressor, binds with the operating gene, so that " theRNA polyme -... 

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