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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...

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...

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...

Prokaryotic Transcriptional Activators and Repressors

Prokaryotic Transcriptional Activators and Repressors

The organization of prokaryotic genes in their genome is notably different from that of eukaryotes. Prokaryotic genes are organized, such that the genes for proteins involved in the same biochemical process or function are located together in groups. This group of genes, along with their regulatory elements, are collectively known as an operon. The functional genes in an operon are transcribed together to give a single strand of mRNA known as polycistronic mRNA.
Transcription of prokaryotic...

Prokaryotic Transcriptional Activators and Repressors

Prokaryotic Transcriptional Activators and Repressors

The organization of prokaryotic genes in their genome is notably different from that of eukaryotes. Prokaryotic genes are organized, such that the genes for proteins involved in the same biochemical process or function are located together in groups. This group of genes, along with their regulatory elements, are collectively known as an operon. The functional genes in an operon are transcribed together to give a single strand of mRNA known as polycistronic mRNA.
Transcription of prokaryotic...

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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DNA-affinity-purified Chip (DAP-chip) Method to Determine Gene Targets for Bacterial Two component Regulatory Systems

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Structure and function of the arginine repressor-operator complex from Bacillus subtilis.

James A Garnett¹, Ferenc Marincs, Simon Baumberg

¹Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK.

Journal of Molecular Biology

|May 6, 2008

Summary

The arginine repressor AhrC in Bacillus subtilis uses its N-terminal domains to bind DNA, with L-arginine controlling gene expression. This study reveals the structural basis for AhrC

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Area of Science:

Bacterial transcriptional regulation
Molecular biology
Structural biology

Background:

L-arginine concentration in bacteria is regulated by transcriptional repressors.
In Bacillus subtilis, AhrC (arginine repressor) controls arginine metabolism genes by interacting with ARG boxes.
AhrC is a hexamer with N-terminal DNA-binding domains and C-terminal L-arginine-binding domains.

Purpose of the Study:

To determine the X-ray crystal structure of the N-terminal domains of AhrC (NAhrC) bound to an ARG box DNA operator.
To analyze the structural basis of DNA binding and sequence specificity for AhrC.
To model the complete AhrC repression complex and understand arginine activation.

Main Methods:

X-ray crystallography to determine the NAhrC-DNA complex structure (2.85 A resolution).
Structural comparison of free and DNA-bound NAhrC N-terminal domains.
Integration of structural data with existing AhrC component structures and transcriptome data.

Main Results:

The structure of the NAhrC dimer bound to an 18 bp ARG box was solved.
Flexible beta-wings of the N-terminal domain stabilize the dimer interface upon DNA binding.
Recognition helices insert into the major groove, wings contact the minor groove, with extensive protein-DNA backbone and base interactions.

Conclusions:

The N-terminal domains of AhrC form a stable dimer on the ARG box, positioning DNA-recognition helices correctly.
Specific interactions between AhrC and the ARG box explain sequence specificity.
A comprehensive model of the AhrC repression complex provides insights into arginine metabolism regulation.