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Related Concept Videos

DNA Topoisomerases02:02

DNA Topoisomerases

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Topoisomerases are enzymes that relax overwound DNA molecules during various cell processes, including DNA replication and transcription. These enzymes regulate positive and negative DNA supercoiling without changing the nucleotide sequence. DNA overwinding in a clockwise direction results in positively supercoiled DNA, whereas underwinding in a counterclockwise direction produces negatively supercoiled DNA.
Types and Mechanism of action
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Conservative Site-specific Recombination and Phase Variation02:53

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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.
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Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

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In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must...
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Single-Strand DNA Binding Proteins01:03

Single-Strand DNA Binding Proteins

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For successful DNA replication, the unwinding of double-stranded DNA must be accompanied by stabilization and protection of the separated single strands of the DNA. This crucial task is performed by single-strand DNA-binding (SSB) proteins. They bind to the DNA in a sequence-independent manner, which means that the nitrogenous bases of the DNA need not be present in a specific order for binding of SSB proteins to it. The binding of SSB proteins straightens single-stranded DNA (ssDNA) and makes...
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DNA as a Genetic Template02:05

DNA as a Genetic Template

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Two structural features of the DNA molecule provide a basis for the mechanisms of heredity: the four nucleotide bases and its double-stranded nature. The Watson-Crick model of double-helical DNA structure, proposed in 1952, drew heavily upon the X-ray crystallography work of researchers Rosalind Franklin and Maurice Wilkins. Watson, Crick, and Wilkins jointly received the Nobel Prize in Physiology or Medicine for their work in 1962. Franklin was, controversially, excluded from the prize for...
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¹H NMR: Interpreting Distorted and Overlapping Signals01:02

¹H NMR: Interpreting Distorted and Overlapping Signals

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Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are...
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Following Cell-fate in E. coli After Infection by Phage Lambda
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Effect of supercoiling on the λ switch.

Kamilla Norregaard1, Magnus Andersson1, Kim Sneppen1

  • 1The Niels Bohr Institute; University of Copenhagen; Copenhagen, Denmark.

Bacteriophage
|January 4, 2014
PubMed
Summary

Supercoiling enhances the efficiency of the bacteriophage lambda (λ) epigenetic switch by increasing DNA looping probability. This mechanism prevents autoregulation interference during induction, ensuring a stable switch between lysogenic and lytic states.

Keywords:
CI proteinPNAcooperativityepigeneticssupercoilingtethered particle motionλ switch

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Studying DNA Looping by Single-Molecule FRET
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Area of Science:

  • Molecular Biology
  • Epigenetics
  • Bacteriophage Genetics

Background:

  • The bacteriophage lambda (λ) switch maintains a stable lysogenic state but can rapidly transition to the lytic state upon DNA damage.
  • The efficiency of this epigenetic switch is crucial for phage lifecycle regulation.

Purpose of the Study:

  • To investigate the effect of DNA supercoiling on the efficiency of the λ epigenetic switch.
  • To understand the role of supercoiling in maintaining the repressed state during induction.

Main Methods:

  • Development of a novel assay using PNA-mediated tethering of a plasmid for single-molecule investigations.
  • Analysis of the influence of supercoiling on CI-mediated DNA looping and epigenetic state transitions.

Main Results:

  • Supercoiling significantly enhances the probability of CI-mediated DNA looping compared to non-supercoiled DNA.
  • The presence of supercoils steepens the transition between looped and unlooped states, increasing the Hill coefficient.
  • The transition occurs at the critical CI concentration required for pRM repression.

Conclusions:

  • DNA supercoiling plays a critical role in maintaining the pRM-repressible state as CI concentration decreases during induction.
  • Supercoiling prevents the autoregulation of the cI gene from interfering with the phage induction process.
  • This mechanism contributes to the stability and responsiveness of the λ epigenetic switch.