Bacteria operon

Yanofsky, C. 1981. Auenuation in the control of expression of bacteria operons. iX ature 289 751 -758,... 

In relatively simple genomes, such as those in bacteria, operons provide a convenient mechanism for regulating genes. Proteins required in the same metabolic pathway or funcdonal process are synthesized together because their genes are controlled by the same promoter. 

Some metals can be converted to a less toxic form through enzyme detoxification. The most well-described example of this mechanism is the mercury resistance system, which occurs in S. aureus,43 Bacillus sp.,44 E. coli,45 Streptomyces lividans,46 and Thiobacillus ferrooxidans 47 The mer operon in these bacteria includes two different metal resistance mechanisms.48 MerA employs an enzyme detoxification approach as it encodes a mercury reductase, which converts the divalent mercury cation into elemental mercury 49 Elemental mercury is more stable and less toxic than the divalent cation. Other genes in the operon encode membrane proteins that are involved in the active transport of elemental mercury out of the cell.50 52... 

In order to produce PHAs in plants it is necessary to introduce the biosynthetic enzymes from bacteria. PHB represents the best characterized and simplest form of PHA, and the synthetic pathway (Figure 4.2) has been extensively studied in Ralstonia eutropha. 30,31 Starting from acetyl-CoA, a P-ketothiolase is required in order to form acetoacetyl-CoA. This is then reduced by a NADPH-dependent acetoacetyl-CoA reductase, which gives rise to 3-hydroxybutyryl-CoA. The latter intermediate is the substrate for the polymerization reaction catalyzed by polyhydroxybutyrate synthase.30 In Ralstonia eutropha, the thiolase, reductase, and synthase genes make up an operon.31... 

Because of their importance in many enzymes, bacteria have had to develop uptake systems for copper and zinc. Copper uptake (and homeostasis, which is discussed in Chapter 8) has been extensively studied in the Gram-positive bacterium Enterococcus hirae. Two of the genes in the cop operon, copA and copB, encode membrane ATPases. An extracellular reductase CorA reduces Cu2+ to Cu+, which is taken up by CopA when copper is limiting. 

The Lac operon (Figure 3.8, described in Esherichia coli bacteria by Jacob and Monod), illustrates how gene expression can be switched on or off according to sudden changes in environmental conditions. Glucose (a monosaccharide) is the preferred... 

The Lac operon is but one example of the genetic adaptations which allow bacteria to respond to their environment. Other examples are to be found in amino acid metabolism, for example the TRP operon which regulates tryptophan metabolism. 

Although Rbr and Rbo are located on separate operons in D. vulgaris, genes encoding Rbo- and Rbr-Uke proteins are located within what appear to be the same operon or gene cluster in several other anaerobic bacteria... 

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