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Operons

Operons

Prokaryotes can control gene expression through operons—DNA sequences consisting of regulatory elements and clustered, functionally related protein-coding genes. Operons use a single promoter sequence to initiate transcription of a gene cluster (i.e., a group of structural genes) into a single mRNA molecule. The terminator sequence ends transcription. An operator sequence, located between the promoter and structural genes, prohibits the operon’s transcriptional activity if bound by a repressor...

Cooperative Binding of Transcription Regulators

Cooperative Binding of Transcription Regulators

Transcriptional regulators bind to specific cis-regulatory sequences in the DNA to regulate gene transcription. These cis-regulatory sequences are very short, usually less than ten nucleotide pairs in length. The short length means that there is a high probability of the exact same sequence randomly occurring throughout the genome. Since regulators can also bind to groups of similar sequences, this further increases the chances of random binding. Transcriptional regulators form dimers that...

Operons

Operons

Prokaryotes can control gene expression through operons—DNA sequences consisting of regulatory elements and clustered, functionally related protein-coding genes. Operons use a single promoter sequence to initiate transcription of a gene cluster (i.e., a group of structural genes) into a single mRNA molecule. The terminator sequence ends transcription. An operator sequence, located between the promoter and structural genes, prohibits the operon’s transcriptional activity if bound by a repressor...

Cooperative Binding of Transcription Regulators

Cooperative Binding of Transcription Regulators

Transcriptional regulators bind to specific cis-regulatory sequences in the DNA to regulate gene transcription. These cis-regulatory sequences are very short, usually less than ten nucleotide pairs in length. The short length means that there is a high probability of the exact same sequence randomly occurring throughout the genome. Since regulators can also bind to groups of similar sequences, this further increases the chances of random binding. Transcriptional regulators form dimers that...

Operon Model

Operon Model

The operon model represents a fundamental mechanism of gene regulation in prokaryotes, enabling coordinated expression of genes involved in related metabolic or functional pathways. Operons consist of structural genes, a promoter, and an operator, with transcription regulated by repressors, activators, and small effector molecules.Structure and Function of OperonsAn operon is a cluster of structural genes transcribed together under the control of a single promoter. The promoter region...

Repressible Operon: trp Operon

Repressible Operon: trp Operon

The trp operon in Escherichia coli exemplifies a repressible operon. It regulates the synthesis of tryptophan through repressor-mediated transcriptional control and attenuation. This dual regulatory mechanism ensures tryptophan biosynthesis occurs only when needed, conserving cellular resources.Structure of the trp OperonThe trp operon consists of five structural genes (trpE, trpD, trpC, trpB, and trpA) that encode enzymes for tryptophan biosynthesis. These genes are transcribed as a single...

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Related Experiment Video

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Single and double loop formation when deoR repressor binds to its natural operator sites.

M Amouyal¹, L Mortensen, H Buc

¹Unité de Physicochimie des Macromolécules Biologiques, URA1149 du CNRS, Institut Pasteur, Paris, France.

|August 11, 1989

Summary

The deoR repressor forms DNA loops to control the deo operon. Electron microscopy visualized these loops, confirming their role in gene repression via cooperative binding at operator sites.

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Area of Science:

Molecular Biology
Genetics
Biophysics

Background:

The deo operon's in vivo repression is linked to the deoR repressor and DNA loop formation.
DNA looping is a key mechanism for regulating gene expression over long distances.

Purpose of the Study:

To investigate the role of the deoR repressor in forming DNA loops.
To visualize and characterize the DNA loop structures mediated by the deoR repressor.
To correlate DNA loop formation with the in vivo repression of the deo operon.

Main Methods:

Electron microscopy was used to visualize DNA-protein complexes.
A DNA fragment containing the deo operon operators was incubated with the oligomeric deoR repressor.
Loop sizes were measured and analyzed.

Main Results:

The deoR repressor formed single DNA loops of specific sizes (280, 600, 880 bp) upon binding to two operators.
Simultaneous binding to three operators resulted in the formation of double loops (280 bp + 600 bp).
Observed loop formation is consistent with long-range repression effects seen in vivo.

Conclusions:

DNA loop formation by the deoR repressor is a direct mechanism for regulating the deo operon.
Cooperative binding of the deoR repressor to all three operator sites is crucial for efficient repression.
Electron microscopy provides visual evidence for the molecular basis of distal gene regulation.