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Related Concept Videos

Homologous Recombination02:31

Homologous Recombination

The basic reaction of homologous recombination (HR) involves two chromatids that contain DNA sequences sharing a significant stretch of identity. One of these sequences uses a strand from another as a template to synthesize DNA in an enzyme-catalyzed reaction. The final product is a novel amalgamation of the two substrates. To ensure an accurate recombination of sequences, HR is restricted to the S and G2 phases of the cell cycle. At these stages, the DNA has been replicated already and the...
Translesion DNA Polymerases02:10

Translesion DNA Polymerases

Translesion (TLS) polymerases rescue stalled DNA polymerases at sites of damaged bases by replacing the replicative polymerase and installing a nucleotide across the damaged site. Doing so, TLS allows additional time for the cell to repair the damage before resuming regular DNA replication.
TLS polymerases are found in all three domains of life - archaea, bacteria, and eukaryotes. Of the different classes of TLS polymerases, members of the Y family are fitted with specialized structures that...
Restarting Stalled Replication Forks02:37

Restarting Stalled Replication Forks

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, a...
Mismatch Repair01:20

Mismatch Repair

Organisms are capable of detecting and fixing nucleotide mismatches that occur during DNA replication. This sophisticated process requires identifying the new strand and replacing the erroneous bases with correct nucleotides. Mismatch repair is coordinated by many proteins in both prokaryotes and eukaryotes.
The Mutator Protein Family Plays a Key Role in DNA Mismatch Repair
The human genome has more than 3 billion base pairs of DNA per cell. Prior to cell division, that vast amount of genetic...
Mismatch Repair01:36

Mismatch Repair

Overview
DNA Damage can Stall the Cell Cycle02:36

DNA Damage can Stall the Cell Cycle

In response to DNA damage, cells can pause the cell cycle to assess and repair the breaks. However, the cell must check the DNA at certain critical stages during the cell cycle. If the cell cycle pauses before DNA replication, the cells will contain twice the amount of DNA. On the other hand, if cells arrest after DNA replication but before mitosis, they will contain four times the normal amount of DNA. With a host of specialized proteins at their disposal,cells must use the right protein at...

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Related Experiment Video

Updated: Jun 12, 2026

Detection of Homologous Recombination Intermediates via Proximity Ligation and Quantitative PCR in Saccharomyces cerevisiae
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Detection of Homologous Recombination Intermediates via Proximity Ligation and Quantitative PCR in Saccharomyces cerevisiae

Published on: September 11, 2022

Semirandom DNA adducts regulate a filamentous defense-associated reverse transcriptase.

Nolan Neville1, Nicole V Johnson2, Edwin E Escobar1

  • 1New England Biolabs Inc., Ipswich, MA, USA.

Nature Structural & Molecular Biology
|June 10, 2026
PubMed
Summary

Defense-associated reverse transcriptases (DRTs) create semirandom DNA for bacteriophage defense. The DRT1 system uses template-free synthesis, forming filaments that inactivate its activity, revealing a novel defense mechanism.

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Real-time Observation of the DNA Strand Exchange Reaction Mediated by Rad51
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Last Updated: Jun 12, 2026

Detection of Homologous Recombination Intermediates via Proximity Ligation and Quantitative PCR in Saccharomyces cerevisiae
07:55

Detection of Homologous Recombination Intermediates via Proximity Ligation and Quantitative PCR in Saccharomyces cerevisiae

Published on: September 11, 2022

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Published on: February 13, 2019

Area of Science:

  • Microbiology
  • Molecular Biology
  • Structural Biology

Background:

  • Bacteriophage defense systems utilize non-genomic DNA synthesis for immunity.
  • The mechanisms by which undefined DNA sequences confer antiphage defense remain unclear.

Purpose of the Study:

  • To elucidate the structure and function of the DRT1 antiphage defense system.
  • To understand how DRT1 synthesizes non-genomic DNA and regulates its activity.

Main Methods:

  • Cryo-electron microscopy (cryo-EM) for structural determination.
  • Biochemical assays to characterize DNA synthesis and enzyme activity.
  • Analysis of bacteriophage escape mutants.

Main Results:

  • DRT1 performs template-free, protein-primed DNA synthesis, generating semirandom DNA adducts.
  • DNA synthesis activates the nitrilase domain, and adducts induce quiescent filament formation.
  • Filamentous DRT1 features domain-swapped C termini forming pseudoknots, occluding active sites and causing dormancy.
  • A T4 single-stranded DNA helicase is essential for DRT1 activity.

Conclusions:

  • DRT1 functions as a minimal retron, integrating reverse transcriptase, effector, and non-genomic antitoxin DNA production.
  • The self-assembly into dormant filaments is a key regulatory mechanism for DRT1 activity.
  • Understanding DRT1 provides insights into novel bacteriophage defense strategies and DNA synthesis mechanisms.