Related Experiment Video

Updated: Aug 2, 2026

Identifying the Effects of BRCA1 Mutations on Homologous Recombination using Cells that Express Endogenous Wild-type BRCA1
08:53

Identifying the Effects of BRCA1 Mutations on Homologous Recombination using Cells that Express Endogenous Wild-type BRCA1

Published on: February 17, 2011

Homologous recombination in extrachromosomal plasmid substrates is not suppressed by p53

H Willers1, E E McCarthy, P Hubbe

  • 1Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA 02129, USA.

Carcinogenesis
|November 8, 2001
PubMed

Insights

The tumor suppressor p53 does not affect extrachromosomal homologous recombination, unlike its known role in chromosomal DNA repair. This suggests p53

Area of Science:

  • Molecular Biology
  • Genetics
  • DNA Repair Mechanisms

Background:

  • The tumor suppressor p53 is known to down-regulate spontaneous homologous recombination in chromosomal DNA.
  • The precise role of p53 in homology-dependent repair of DNA double-strand breaks, especially in extrachromosomal contexts, remains unclear.
  • Previous hypotheses suggested p53 might directly interact with recombination intermediates to suppress homologous recombination.

Purpose of the Study:

  • To investigate whether p53 suppresses extrachromosomal homologous recombination, both spontaneous and induced by DNA double-strand breaks.
  • To determine if p53 influences homology-dependent repair pathways in extrachromosomal substrates.
  • To compare the impact of p53 status on homologous and non-homologous recombination frequencies in extrachromosomal DNA.

Main Methods:

  • Utilized a plasmid shuttle assay with episomally replicating substrates containing mutated tandem repeats of a CAT reporter gene.
  • Induced DNA double-strand breaks using the I-SceI nuclease to study homology-dependent repair.
  • Employed isogenic mouse fibroblast lines with varying p53 status to assess its effect on recombination.

Main Results:

  • Extrachromosomal homologous recombination occurred independently of the p53 status of the cell lines.
  • This independence was observed for both Rad51-independent single-strand annealing and Rad51-dependent gene conversion pathways.
  • Homologous and non-homologous recombination contributed similarly to the repair of induced double-strand breaks, regardless of p53 status.

Conclusions:

  • p53-mediated regulation of homologous recombination appears to be specific to the ordered chromosomal chromatin structure.
  • Extrachromosomal DNA repair models may not fully recapitulate p53's regulatory functions observed in chromosomal contexts.
  • Caution is advised when using solely extrachromosomal systems to study DNA repair mechanisms in intact cells.

More Related Videos

Preparation of the Mgm101 Recombination Protein by MBP-based Tagging Strategy11:40

Preparation of the Mgm101 Recombination Protein by MBP-based Tagging Strategy

Published on: June 25, 2013

Yeast As a Chassis for Developing Functional Assays to Study Human P5314:57

Yeast As a Chassis for Developing Functional Assays to Study Human P53

Published on: August 4, 2019

Related Concept Videos

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...
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...
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...
Abnormal Proliferation02:23

Abnormal Proliferation

Under normal conditions, most adult cells remain in a non-proliferative state unless stimulated by internal or external factors to replace lost cells. Abnormal cell proliferation is a condition in which the cell's growth exceeds and is uncoordinated with normal cells. In such situations, cell division persists in the same excessive manner even after cessation of the stimuli, leading to persistent tumors. The tumor arises from the damaged cells that replicate to pass the damage to the daughter...
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...
Crossing Over01:30

Crossing Over

Crossing over is the exchange of genetic information between homologous chromosomes during prophase I of meiosis I. Genetic recombination gives rise to allelic diversity in the newly formed daughter cells. In humans, crossing over produces genetically distinct haploid egg and sperm cells that undergo fertilization to produce unique offspring. Before cell division starts, the germ cell’s chromosome(s) undergo duplication in the S phase of the cell cycle. As the cells enter prophase I, duplicated...