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Related Concept Videos

Inducible Operons: lac Operon01:25

Inducible Operons: lac Operon

The lac operon in Escherichia coli is a model for understanding inducible gene regulation and metabolic flexibility. It integrates local control by lactose and global regulation through catabolite repression, enabling E. coli to preferentially metabolize glucose when available and switch to lactose utilization when glucose is scarce.Structure and Function of the lac OperonThe lac operon contains three structural genes: lacZ (β-galactosidase), lacY (lactose permease), and lacA (thiogalactoside...
Cooperative Binding of Transcription Regulators02:13

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...
Operons02:09

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...
Co-activators and Co-repressors02:04

Co-activators and Co-repressors

Gene transcription is regulated by the synergistic action of several proteins that form a complex at a gene regulatory site. This is observed in eukaryotes, where the regulation of gene expression is a complex process. Regulatory proteins in eukaryotes can broadly be classified into two types – regulators that bind directly to specific DNA sequences and co-regulators that associate with regulatory proteins but cannot directly bind to the DNA. These co-regulators are further divided into...
Operon Model01:23

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...
Conservative Site-specific Recombination and Phase Variation02:53

Conservative Site-specific Recombination and Phase Variation

Because the DNA segments are cut and reorganized in a direction-specific manner, site-specific recombination has emerged as an efficient genetic engineering technique. Flippase and Cyclization recombinases or Flp and Cre, respectively, are two members of the tyrosine recombinase family derived from bacteriophages, that are used to mediate site-specific DNA insertions, deletions, and targeted expression of proteins in mammalian cell lines.
The recognition sites for Cre recombinase called LoxP...

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Related Experiment Video

Updated: Jun 29, 2026

Combining Single-molecule Manipulation and Imaging for the Study of Protein-DNA Interactions
14:43

Combining Single-molecule Manipulation and Imaging for the Study of Protein-DNA Interactions

Published on: August 27, 2014

Interconvertible lac repressor-DNA loops revealed by single-molecule experiments.

Oi Kwan Wong1, Martin Guthold, Dorothy A Erie

  • 1Department of Biochemistry, Brandeis University, Waltham, Massachusetts, USA.

Plos Biology
|October 3, 2008
PubMed
Summary
This summary is machine-generated.

Escherichia coli lactose repressor forms small, stable DNA loops. Individual complexes dynamically switch between two distinct loop structures, suggesting a mechanism for robust transcription regulation.

More Related Videos

Studying DNA Looping by Single-Molecule FRET
11:27

Studying DNA Looping by Single-Molecule FRET

Published on: June 28, 2014

Related Experiment Videos

Last Updated: Jun 29, 2026

Combining Single-molecule Manipulation and Imaging for the Study of Protein-DNA Interactions
14:43

Combining Single-molecule Manipulation and Imaging for the Study of Protein-DNA Interactions

Published on: August 27, 2014

Studying DNA Looping by Single-Molecule FRET
11:27

Studying DNA Looping by Single-Molecule FRET

Published on: June 28, 2014

Area of Science:

  • Molecular biology
  • Biophysics
  • Structural biology

Background:

  • Transcription regulation often involves proteins binding multiple DNA sites, forming loops.
  • The structures and dynamics of these transcription factor-mediated DNA loops are not well understood.

Purpose of the Study:

  • To investigate the in vitro loop formation mediated by Escherichia coli lactose repressor.
  • To elucidate the structures and dynamics of these DNA loops using single-molecule methods.

Main Methods:

  • Single-molecule structural and kinetics methods were employed.
  • In vitro loop formation by Escherichia coli lactose repressor was directly examined.

Main Results:

  • Small (approx. 150 bp) DNA loops formed rapidly and stably, irrespective of operator spacing.
  • Individual protein-DNA complexes exhibited spontaneous transitions between two distinct loop structures.
  • A dynamic equilibrium was identified between a novel V-shaped repressor conformation and a more linear conformation, reducing DNA bending strain.

Conclusions:

  • The lactose repressor can adopt multiple loop structures, indicating conformational flexibility.
  • This structural plasticity may explain how transcription regulation remains robust despite varying mechanical energy requirements for loop formation.