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Chapter 7 : Control of Gene Expression by Compartmentalization: the Operon

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Control of Gene Expression by Compartmentalization: the Operon, Page 1 of 2

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Abstract:

In this chapter, the author tells a story about the characterization of the operon from . The author commenced his research trying to figure out why high phosphate concentrations inhibit cell division in . In the final analysis, the most obvious change was in the distribution of phospholipids; however, it was not clear if this was the reason why cells stopped dividing or a secondary response to the inhibition of cell division. This led to his lifelong interest in membranes and convinced him that if he wanted to understand cause and effect, he will need to do genetics. His research in John’s lab focused on the regulation of proline utilization by the PutA protein, a bifunctional protein that could function as either a membrane-associated enzyme or a repressor. The proline utilization () operon allows cells to use proline as a sole source of carbon, nitrogen, and energy. In vitro studies confirmed that PutA binds to specific operator sites in the control region. Instead of simply responding to the presence or absence of proline, induction of the operon requires several physiological conditions needed for its catabolism: high concentrations of proline, an appropriate terminal electron acceptor, and the absence of other substrates that could compete for functional membrane binding sites.

Citation: Maloy S. 2011. Control of Gene Expression by Compartmentalization: the Operon, p 55-63. In Maloy S, Hughes K, Casadesús J (ed), The Lure of Bacterial Genetics. ASM Press, Washington, DC. doi: 10.1128/9781555816810.ch7

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Electron Transport System
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Fatty Acid Degradation
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Bacterial Proteins
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Atomic Force Microscopy
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Figures

Image of FIGURE 1
FIGURE 1

Proline utilization pathway. Proline is transported by the gene product, a sodium-proline sym-porter. Once inside the cell, proline is degraded in two enzymatic steps by the gene product, a multifunctional protein with proline-FAD dehydrogenase (i) and P5C-NAD dehydrogenase (ii) activities.

Citation: Maloy S. 2011. Control of Gene Expression by Compartmentalization: the Operon, p 55-63. In Maloy S, Hughes K, Casadesús J (ed), The Lure of Bacterial Genetics. ASM Press, Washington, DC. doi: 10.1128/9781555816810.ch7
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Image of FIGURE 2
FIGURE 2

control region. The and genes are divergently transcribed from promoters within the 420-bp region located between the and translation start sites. Gray arrows represent the and promoters. Rectangles labeled to represent PutA binding sites (“operator sites”). Dark rectangles indicate IHF binding sites. The squiggle to the left of represents a strong intrinsic bend.

Citation: Maloy S. 2011. Control of Gene Expression by Compartmentalization: the Operon, p 55-63. In Maloy S, Hughes K, Casadesús J (ed), The Lure of Bacterial Genetics. ASM Press, Washington, DC. doi: 10.1128/9781555816810.ch7
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Image of FIGURE 3
FIGURE 3

Model for the physiological regulation of proline utilization. At low intracellular proline, PutA is cytoplasmic and functions as a transcriptional repressor of the operon. As the concentration of proline increases, the FAD cofactor in PutA is reduced and proline is converted to P5C. Reduction of FAD alters the conformation of PutA and increases its hydrophobicity. The increased hydrophobicity drives PutA to the inner leaflet of the cytoplasmic membrane (CM) where it cannot bind DNA but functions as an enzyme. As proline levels decrease due to degradation, the FADH is reoxidized and PutA regains its dimeric, hydrophilic structure. Consequently, PutA accumulates in the cytoplasm and represses transcription of the operon. (Note that the higher order structure of the repressing protein-DNA complex and phosphorylation of PutA are not shown in this figure.)

Citation: Maloy S. 2011. Control of Gene Expression by Compartmentalization: the Operon, p 55-63. In Maloy S, Hughes K, Casadesús J (ed), The Lure of Bacterial Genetics. ASM Press, Washington, DC. doi: 10.1128/9781555816810.ch7
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References

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