Prokaryotes enhancers

Devos, D., J. Garmendia, V. de Lorenzo, and A. Valencia. 2002. Deciphering the action of aromatic effectors on the prokaryotic enhancer-binding protein XylR A structural model of its N-terminal domain. Environ Microbiol 4 29-41. 

Activator proteins (and a few repressors) are important in eukaryotes, as they are in prokaryotes. The DNA sequences to which activator proteins bind in eiikaryotic DNA are called response elements. A few response elements are located within the promoter region (upstream promoter elements [UPE]), but most are outside the promoter and often clustered to form an enhancer region that allows control of gene expression by multiple signals (Figure 1-5-4). 

The nomenclature for transcription factors is confusing. Depending on their mode of action, various terms are in use both for the proteins themselves and for the DNA sequences to which they bind. If a factor blocks transcription, it is referred to as a repressor otherwise, it is called an inducer. DNA sequences to which regulatory proteins bind are referred to as control elements. In prokaryotes, control elements that serve as binding sites for RNA polymerases are called promoters, whereas repressor-binding sequences are usually called operators. Control elements that bind activating factors are termed enhancers, while elements that bind inhibiting factors are known as silencers. 

Kustu, S., A. K. North, and D. S. Weiss, Prokaryotic transcriptional enhancers and enhancer-binding proteins. Trends Biochem. Sci. 16 397-401, 1991. First discovered in eukaryotes, enhancers have now been found to exist for a number of prokaryotic genes. 

A strong influence on the biosynthesis of peptide metabolites exerted by exogenously supplied amino-acid precursors has been observed earlier both in prokaryotes and eukaryotes [26]. In several cases, enhanced yields of a desired metabolite can be obtained and a replacement of certain constitutional building elements by other amino acids may occur [27, 28]. 

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