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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/Cas9 Genome Editing01:28

CRISPR/Cas9 Genome Editing

The CRISPR-Cas system serves as a bacterial defense mechanism against invading genetic elements such as viruses and plasmids, forming the foundation for its adaptation as a powerful genome-editing tool. Originally discovered in prokaryotes, this system has been repurposed to revolutionize genetic engineering across a wide range of organisms, including plants, animals, and humans. The core component, Cas9, is an endonuclease derived from Streptococcus pyogenes, capable of introducing...
Covalently Linked Protein Regulators02:04

Covalently Linked Protein Regulators

Proteins can undergo many types of post-translational modifications, often in response to changes in their environment. These modifications play an important role in the function and stability of these proteins. Covalently linked molecules include functional groups, such as methyl, acetyl, and phosphate groups, and also small proteins, such as ubiquitin. There are around 200 different types of covalent regulators that have been identified.
These groups modify specific amino acids in a protein.
Spreading of Chromatin Modifications02:25

Spreading of Chromatin Modifications

The histone proteins in the nucleosomes are post-translationally modified (PTM) to increase or decrease access to DNA. The commonly observed PTMs are methylation, acetylation, phosphorylation, and ubiquitination of lysine amino acids in the histone H3 tail region. These histone modifications have specific meaning for the cell. Hence, they are called "histone code". The protein complex involved in histone modification is termed as "reader-writer" complex.
Writers
The writer is an enzyme that can...
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...

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Related Experiment Video

Updated: May 9, 2026

In Vitro Directed Evolution of a Restriction Endonuclease with More Stringent Specificity
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Published on: March 25, 2020

Type III restriction-modification enzymes: a historical perspective.

Desirazu N Rao1, David T F Dryden, Shivakumara Bheemanaik

  • 1Department of Biochemistry, Indian Institute of Science, Bangalore 560 012, India and School of Chemistry, The King's Buildings, The University of Edinburgh, Edinburgh EH9 3JJ, Scotland, UK.

Nucleic Acids Research
|July 19, 2013
PubMed
Summary

Type III restriction-modification systems use two DNA recognition sites for cleavage, requiring ATP hydrolysis for communication. These systems are crucial in bacteria, influencing virulence in pathogens.

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Last Updated: May 9, 2026

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Published on: March 25, 2020

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Area of Science:

  • Molecular Biology
  • Biochemistry

Background:

  • Restriction-modification (R-M) systems protect bacterial DNA from cleavage by restriction endonucleases via DNA methyltransferases.
  • R-M systems are classified into four types based on structure, DNA recognition, cleavage site, and cofactor needs.

Observation:

  • Type III R-M enzymes require two separate, unmethylated DNA sequences in a head-to-head orientation for efficient cleavage.
  • Cleavage occurs 25-27 bp downstream of one recognition site.
  • Type III R-M enzymes, similar to Type I, exhibit sequence-specific ATPase activity essential for DNA cleavage.

Findings:

  • ATP hydrolysis fuels long-distance communication between the two DNA recognition sites.
  • Models involving 1D diffusion and 3D DNA looping explain the interaction between distant recognition sites.
  • Type III R-M systems are widespread in bacteria, including pathogenic species where they can be phase-variable and contribute to virulence.

Implications:

  • Understanding Type III R-M systems provides insights into DNA recognition and catalytic mechanisms.
  • Further biochemical, genetic, and structural studies promise detailed mechanistic understanding.
  • The role of phase-variable Type III R-M systems in bacterial virulence warrants further investigation.