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Related Concept Videos

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...
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...
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DNA replication is initiated at sites containing predefined DNA sequences known as origins of replication. DNA is unwound at these sites by the minichromosome maintenance (MCM) helicase and other factors such as Cdc45 and the associated GINS complex.The unwound single strands are protected by replication protein A (RPA) until DNA polymerase starts synthesizing DNA at the 5’ end of the strand in the same direction as the replication fork. To prevent the replication fork from falling apart, a...
Eukaryotic Transcription Inhibitors01:52

Eukaryotic Transcription Inhibitors

Certain biochemical processes, such as embryonic development and cell growth regulation, depend on the repression of specific genes. DNA binding proteins known as eukaryotic transcription inhibitors regulate the repression of gene expression in eukaryotes. The presence of these inhibitors at the required location and time in the cell is triggered by the presence of hormones and additional signals from other cells.
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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...
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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.
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Related Experiment Video

Updated: Jun 20, 2026

Studying DNA Looping by Single-Molecule FRET
11:27

Studying DNA Looping by Single-Molecule FRET

Published on: June 28, 2014

AFM studies of lambda repressor oligomers securing DNA loops.

Haowei Wang1, Laura Finzi, Dale E A Lewis

  • 1Department of Cell Biology, Emory University, Atlanta, GA 30322, USA.

Current Pharmaceutical Biotechnology
|August 20, 2009
PubMed
Summary
This summary is machine-generated.

Lambda bacteriophage repressor protein (CI) forms DNA loops to control gene expression. Scanning force microscopy revealed specific oligomer sizes sealing these loops, clarifying the lysogenic state maintenance.

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Area of Science:

  • Molecular Biology
  • Genetics
  • Biophysics

Background:

  • Bacteriophage lambda can enter lytic or lysogenic growth cycles.
  • The lysogenic state is maintained by the lambda repressor (CI) binding to operator sites, repressing lytic promoters.
  • Protein-DNA looping is implicated in regulating gene expression and developmental pathways.

Purpose of the Study:

  • To investigate the oligomerization of lambda repressor (CI) in looped DNA structures.
  • To determine the specific oligomer sizes that seal DNA loops formed by CI.
  • To understand the role of CI oligomerization in maintaining the lysogenic state.

Main Methods:

  • Scanning force microscopy (SFM) was employed to directly visualize DNA-protein complexes.
  • Tethered particle motion analysis was used previously to study looping equilibrium but could not resolve oligomerization.
  • SFM allowed determination of operator site occupancies for looped and unlooped conformations.

Main Results:

  • An equilibrium between looped and unlooped DNA molecules was observed.
  • Specific operator site occupancies were determined for various looped and unlooped conformations.
  • DNA loops were found to be sealed by CI oligomers of varying sizes: 6-8, 10-12, and 14-16 units.

Conclusions:

  • Scanning force microscopy provides high-resolution insights into protein-DNA interactions and looping.
  • The size of CI oligomers sealing DNA loops directly correlates with specific conformations.
  • These findings elucidate the molecular mechanisms underlying the stable maintenance of the lambda phage lysogenic state.