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Related Concept Videos

Restriction Enzymes01:11

Restriction Enzymes

Restriction enzymes are bacterial enzymes used to cut DNA in a sequence-specific manner. To cleave DNA, they bind to specific palindromic sequences called restriction sites. Such palindromic DNA sequences or inverted repeats are commonly found in regions of functional significance, such as the origin of replication, gene operator sites, and regions containing transcription termination signals.
The host bacteria protect their own genomic DNA from these enzymes by methylating these sites. Some...
Inhibitors of Bacterial DNA Synthesis01:28

Inhibitors of Bacterial DNA Synthesis

Bacterial pathogens depend on precise and efficient DNA replication to sustain infection. Two type II topoisomerases—DNA gyrase and topoisomerase IV—are critical to this process, as they resolve DNA supercoiling and unlink chromosomes during replication. Fluoroquinolones, synthetic derivatives of quinolones, exploit this mechanism by stabilizing the transient DNA–enzyme cleavage complex, preventing strand religation, and causing lethal double-strand breaks. These antibiotics are selectively...
DNA Topoisomerases02:02

DNA Topoisomerases

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
Topoisomerases are divided into two main types.  Type I...
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...
CRISPR and crRNAs02:53

CRISPR and crRNAs

Bacteria and archaea are susceptible to viral infections just like eukaryotes; therefore, they have developed a unique adaptive immune system to protect themselves. Clustered regularly interspaced short palindromic repeats and CRISPR-associated proteins (CRISPR-Cas) are present in more than 45% of known bacteria and 90% of known archaea.
The CRISPR-Cas system stores a copy of foreign DNA in the host genome and uses it to identify the foreign DNA upon reinfection. CRISPR-Cas has three different...
Ribozymes02:47

Ribozymes

The term ribozyme is used for RNA that can act as an enzyme. Ribozymes are mainly found in selected viruses, bacteria, plant organelles, and lower eukaryotes. Ribozymes were first discovered in 1982 when Tom Cech’s laboratory observed Group I introns acting as enzymes. This was shortly followed by the discovery of another ribozyme, Ribonulcease P, by Sid Altman’s laboratory. Both Cech and Altman received the Nobel Prize in chemistry in 1989 for their work on ribozymes.
Ribozymes can be...

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Related Experiment Video

Updated: Jun 14, 2026

In Vitro Directed Evolution of a Restriction Endonuclease with More Stringent Specificity
09:16

In Vitro Directed Evolution of a Restriction Endonuclease with More Stringent Specificity

Published on: March 25, 2020

The type IIB restriction endonucleases.

Jacqueline J T Marshall1, Stephen E Halford

  • 1The DNA-Protein Interactions Unit, Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK. jacqui.marshall@bristol.ac.uk

Biochemical Society Transactions
|March 20, 2010
PubMed
Summary
This summary is machine-generated.

Type IIB restriction enzymes uniquely cleave DNA on both sides of their recognition site, liberating a short DNA fragment. This review covers current knowledge of these distinct restriction-modification systems.

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Single-Molecule Dwell-Time Analysis of Restriction Endonuclease-Mediated DNA Cleavage
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Single-Molecule Dwell-Time Analysis of Restriction Endonuclease-Mediated DNA Cleavage

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CAPRRESI: Chimera Assembly by Plasmid Recovery and Restriction Enzyme Site Insertion
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CAPRRESI: Chimera Assembly by Plasmid Recovery and Restriction Enzyme Site Insertion

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Related Experiment Videos

Last Updated: Jun 14, 2026

In Vitro Directed Evolution of a Restriction Endonuclease with More Stringent Specificity
09:16

In Vitro Directed Evolution of a Restriction Endonuclease with More Stringent Specificity

Published on: March 25, 2020

Single-Molecule Dwell-Time Analysis of Restriction Endonuclease-Mediated DNA Cleavage
09:53

Single-Molecule Dwell-Time Analysis of Restriction Endonuclease-Mediated DNA Cleavage

Published on: February 7, 2021

CAPRRESI: Chimera Assembly by Plasmid Recovery and Restriction Enzyme Site Insertion
07:37

CAPRRESI: Chimera Assembly by Plasmid Recovery and Restriction Enzyme Site Insertion

Published on: June 25, 2017

Area of Science:

  • Molecular Biology
  • Enzymology
  • Genetics

Background:

  • Restriction-modification systems are crucial for DNA metabolism and defense.
  • Type IIB restriction enzymes represent a unique subclass within Type II restriction enzymes.
  • These enzymes share organizational and assembly characteristics with Type I systems, despite Type II classification.

Purpose of the Study:

  • To review and consolidate current knowledge on Type IIB restriction-modification systems.
  • To highlight the unique enzymatic properties of Type IIB endonucleases.
  • To compare Type IIB systems with other restriction-modification enzyme classes.

Main Methods:

  • Literature review of existing research on Type IIB restriction-modification systems.
  • Comparative analysis of Type IIB enzymes with Type I and other Type II systems.
  • Examination of gene organization and protein assembly in Type IIB systems.

Main Results:

  • Type IIB endonucleases cleave both DNA strands at specific sites distant from their recognition sequences.
  • A key characteristic is cleavage on both sides of the recognition site, releasing a short DNA duplex.
  • Despite being Type II, their gene organization and protein assembly resemble Type I systems.

Conclusions:

  • Type IIB restriction enzymes possess unique biochemical and organizational features.
  • Further research is needed to fully elucidate the mechanisms and biological roles of Type IIB systems.
  • Understanding Type IIB systems provides insights into the diversity of DNA modification and restriction mechanisms.