Related Experiment Video
Updated: Jul 4, 2025
07:50
Plasmid-derived DNA Strand Displacement Gates for Implementing Chemical Reaction Networks
Published on: November 25, 2015
14.4K
Structural basis for plasmid restriction by SMC JET nuclease
Florian Roisné-Hamelin1, Hon Wing Liu1, Michael Taschner1
1Department of Fundamental Microbiology (DMF), Faculty of Biology and Medicine (FBM), University of Lausanne (UNIL), 1015 Lausanne, Switzerland.
Molecular Cell
|February 3, 2024
Summary
Prokaryotic SMC Wadjet (JET) complexes eliminate plasmids by cleaving DNA. This study reveals JET recognizes plasmids by mechanical bending of unextruded DNA, a key step in DNA immunity.
Area of Science:
- Molecular Biology
- Structural Biology
- Genetics
Background:
- DNA loop-extruding SMC complexes are vital for chromosome organization and DNA immunity in cells.
- Prokaryotic SMC Wadjet (JET) complexes prevent plasmid spread via DNA cleavage, but recognition mechanisms remain unclear.
Purpose of the Study:
- To elucidate the mechanism of plasmid recognition and DNA cleavage by prokaryotic SMC Wadjet (JET) complexes.
- To understand how JET complexes distinguish foreign (plasmid) DNA from self (chromosomal) DNA.
Main Methods:
- Investigated DNA cleavage by JET complexes using circularized and immobilized DNA substrates.
- Determined the structures of plasmid-bound JetABC complexes using cryo-electron microscopy.
- Analyzed the role of JetD nuclease in processing the DNA substrate.
Main Results:
- Artificial circularization made linear DNA susceptible to JET cleavage.
- JET specifically cleaved immobilized plasmid DNA at an anchoring point, hindering extrusion but not cleavage.
- Structures revealed stalled SMC motor units entrapping U-shaped DNA, converted to a V-shaped substrate by JetD.
Conclusions:
- Mechanical bending of residual unextruded DNA serves as a molecular signature for plasmid recognition by JET.
- This mechanism facilitates non-self DNA elimination, contributing to bacterial DNA immunity.
- Key aspects of SMC loop extrusion, including motor direction and DNA-holding states, were elucidated.
Related Concept Videos
01:11Restriction Enzymes
30.7K
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...
The host bacteria protect their own genomic DNA from these enzymes by methylating these sites. Some...
30.7K
01:03Single-Strand DNA Binding Proteins
14.1K
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...
14.1K
02:53Conservative Site-specific Recombination and Phase Variation
6.0K
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...
The recognition sites for Cre recombinase called LoxP...
6.0K
01:45Regulation of Nuclear Protein Sorting
2.4K
Nuclear protein sorting regulates nucleus composition and gene expression, crucial for determining the fate of a eukaryotic cell. Hence, the entry and exit of molecules across the nuclear envelope is a tightly controlled process. Nuclear protein sorting can be inhibited by one of the following ways: 1) masking cargo signal sequences, 2) modifying the nuclear receptor's affinity for cargo, 3) controlling the nuclear pore size, 4) retaining the cargo during its transit to the cytosol or the...
2.4K
02:53CRISPR and crRNAs
17.0K
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...
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...
17.0K
02:37Restarting Stalled Replication Forks
5.8K
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,...
5.8K