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Chapter VI: Transcription of the Lactose Operon in E. coli

Gérard Contesse, Michel Crépin, François Gros


For the past ten years, the lactose system of E. coli has served as a reference model to study gene expression and its control in micro-organisms. Most of our knowledge about the functioning of this classical system stems from pure genetic studies or chemical or immunological analyses of the enzymes coded for by the structural genes that compose the lac operon.

Relatively little work has been focused on lac-specific mRNA, in spite of the fact that much of our understanding about the regulation of the lac system would benefit from a clear picture about the mechanism whereby it is transcribed into messenger RNA in normal as well as in physiologically or genetically altered conditions.

This latter remark not only applies to the formal study of enzymatic repression mechanisms but to problems such as catabolite repression, polarity effects, role of the promoter sequence as an initiation signal for gene expression and possible coupling between translational and transcriptional processes.

The purpose of this chapter is to survey some of the general properties of the RNA transcription product, resulting from the expression of the lactose region in E. coli and to examine if, and how, we can correlate many of the classically-known effects at the enzyme level, with changes at the messenger RNA level.

Numerous approaches have been used for detecting RNA corresponding to the lac region, some involving direct hybridization techniques, others taking advantage of the enzyme forming capacity of the preinduced messenger. Although...

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