Prokaryotes operons

FIGURE 28-5 Representative prokaryotic operon. Genes A, B, and C are transcribed on one polycistronic mRNA. Typical regulatory sequences include binding sites for proteins that either activate or repress transcription from the promoter. 

We will look more closely at the cyclic-AMP-response element as an example of eukaryotic control of transcription. Hundreds of research papers deal with this topic as more and more genes are found to have this response element as part of their control. Remember that cAMP was also involved in the control of prokaryotic operons via the GAP protein. 

In addition to HMG-CoA synthase, involved in ketogenesis, genes involved in fatty acid activation, like acyl-CoA synthetase," or in p-oxidation, like medium-chain acyl-CoA dehydrogenase are also target of PPAR. This transactivation pathway is reminiscent of a prokaryotic operon organization, in which fatty acids induce the expression of the genes responsible for their metabolism. We speculated that the main control step in fatty acid P-oxidation, the outer membrane component of carnitine palmitoyltransferase enzyme system, CPT I, could also be a PPAR target. 

Answer E. TBP and CBP participate in eukaryotic gene transcription and mRNA translation, respectively. CAP regulates the expression of prokaryotic lactose operons. ACP is involved in fatty add synthesis. 

B. The lac operon of E coli is a good model for regulation of prokaryotic gene expression in response to environmental cues (Figure 12-4). 

Many Prokaryotic Genes Are Clustered and Regulated in Operons... 

One mechanism of transcriptional control in prokaryotes, especially of several operons controlling the biosynthesis of amino acids, is attenuation. 

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. 

Operon. A group of contiguous genes that are coordinately regulated by two cis-acting elements A promoter and an operator. Found only in prokaryotic cells. 

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