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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...
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...
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...
Non-LTR Retrotransposons03:18

Non-LTR Retrotransposons

As the name suggests, non-LTR retrotransposons lack the long terminal repeats characteristic of the LTR retrotransposons. Additionally, both LTR and non-LTR retrotransposons use distinct mechanisms of mobilization. Non-LTR retrotransposons are further divided into two classes - Long interspersed nuclear elements (LINEs) and short interspersed nuclear elements (SINEs), both of which occur abundantly in most mammals, including humans. Some of the active non-LTR retrotransposons in humans are L1...

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Related Experiment Video

Updated: May 7, 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

Type I restriction enzymes and their relatives.

Wil A M Loenen1, David T F Dryden, Elisabeth A Raleigh

  • 1Leiden University Medical Center, P.O. Box 9600, 2300 RC, Leiden, The Netherlands, EastChem School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9, 3JJ, Scotland, UK and New England Biolabs Inc., 240 County Road Ipswich, MA 01938-2723, USA.

Nucleic Acids Research
|September 27, 2013
PubMed
Summary

Type I restriction enzymes (REases) are complex proteins with unique DNA sequence recognition abilities. Despite past challenges, ongoing research is revealing their biochemistry, biology, and potential applications in molecular biology.

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Single-Molecule Dwell-Time Analysis of Restriction Endonuclease-Mediated DNA Cleavage
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Last Updated: May 7, 2026

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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

Area of Science:

  • Molecular Biology
  • Biochemistry
  • Genetics

Background:

  • Type I restriction enzymes (REases) are large, pentameric proteins composed of distinct restriction (R), methylation (M), and DNA sequence-recognition (S) subunits.
  • Historically, Type I REases have been difficult to characterize, limiting their use in molecular biology compared to Type II REases.

Purpose of the Study:

  • To provide a comprehensive overview of Type I REases, including their biochemistry, biology, and regulation.
  • To explore the mechanisms of evasion employed by bacteriophages and plasmids against Type I REases.
  • To discuss the remarkable sequence specificity changes in Type I REases due to domain shuffling and rearrangements.

Main Methods:

  • Genome analysis to identify Type I REase genes.
  • Methylome analysis to determine DNA recognition sequences.
  • Review of classic experiments and current studies on Type I REase biochemistry and function.

Main Results:

  • Genome and methylome analyses are facilitating the characterization of Type I REases.
  • Type I REases exhibit remarkable sequence specificity plasticity through domain shuffling.
  • Bacteriophages and plasmids have evolved sophisticated strategies to evade Type I REase activity.

Conclusions:

  • Type I REases possess unique features, including adaptable sequence specificity, warranting greater attention.
  • Understanding Type I REases and their interaction with mobile genetic elements offers insights into microbial defense mechanisms.
  • Similarities exist between Type I enzymes and certain Type II restriction-modification systems, particularly Type IIG enzymes.