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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...
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...
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...
Inheritance of Chromatin Structures03:17

Inheritance of Chromatin Structures

Epigenetics is the study of inherited changes in a cell's phenotype without changing the DNA sequences. It provides a form of memory for the differential gene expression pattern to maintain cell lineage, position-effect variegation, dosage compensation, and maintenance of chromatin structures such as telomeres and centromeres. For example, the structure and location of the centromere on chromosomes are epigenetically inherited. Its functionality is not dictated or ensured by the underlying DNA...
Fixing Double-strand Breaks02:04

Fixing Double-strand Breaks

The double-stranded structure of DNA has two major advantages. First, it serves as a safe repository of genetic information where one strand serves as the back-up in case the other strand is damaged. Second, the double-helical structure can be wrapped around proteins called histones to form nucleosomes, which can then be tightly wound to form chromosomes. This way, DNA chains up to 2 inches long can be contained within microscopic structures in a cell. A double-stranded break not only damages...
Nucleotide Excision Repair01:08

Nucleotide Excision Repair

Overview

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Atomic Force Microscopy Investigations of DNA Lesion Recognition in Nucleotide Excision Repair
10:59

Atomic Force Microscopy Investigations of DNA Lesion Recognition in Nucleotide Excision Repair

Published on: May 24, 2017

A human XRCC4-XLF complex bridges DNA.

Sara N Andres1, Alexandra Vergnes, Dejan Ristic

  • 1Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON L8N 3Z5, Canada.

Nucleic Acids Research
|January 31, 2012
PubMed
Summary

The XRCC4-XLF complex bridges DNA molecules, revealing an early role in non-homologous end joining (NHEJ) independent of DNA Ligase IV. This finding clarifies complex formation and DNA interactions in DNA repair.

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Deciphering High-Resolution 3D Chromatin Organization via Capture Hi-C
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Deciphering High-Resolution 3D Chromatin Organization via Capture Hi-C

Published on: October 14, 2022

Area of Science:

  • Molecular Biology
  • Genetics
  • Biochemistry

Background:

  • DNA double-strand breaks (DSBs) are critical threats to cell survival.
  • Non-homologous end joining (NHEJ) is the primary repair pathway for DSBs in higher eukaryotes.
  • XRCC4 and XLF are key proteins within the NHEJ pathway.

Purpose of the Study:

  • To elucidate the mechanism by which XRCC4-XLF complexes bridge DNA molecules.
  • To investigate the role of XRCC4-XLF in the early stages of NHEJ.
  • To identify specific functions of XRCC4-XLF C-terminal tails in complex formation and interactions.

Main Methods:

  • DNA-binding and DNA-bridging assays.
  • Direct visualization techniques.
  • Mutational analysis of XRCC4-XLF C-terminal regions.
  • Crystal structure determination of XRCC4-XLF filaments.

Main Results:

  • XRCC4-XLF complexes exhibit robust DNA bridging activity, independent of DNA Ligase IV.
  • This bridging suggests an early function for XRCC4-XLF in the NHEJ pathway.
  • Mutations in C-terminal tails reveal specialized roles in complex assembly and interactions with DNA and DNA Ligase IV.
  • A 3.94 Å crystal structure shows an extended XRCC4-XLF protein filament.

Conclusions:

  • XRCC4-XLF plays a crucial, previously unrecognized early role in DNA bridging during NHEJ.
  • The C-terminal regions of XRCC4-XLF are critical for its assembly and interactions within the NHEJ machinery.
  • A structural model for XRCC4-XLF function in NHEJ is proposed, integrating bridging and ligation steps.